Bulletin of the Global Volcanism Network

All reports of volcanic activity published by the Smithsonian since 1968 are available through a monthly table of contents or by searching for a specific volcano. Until 1975, reports were issued for individual volcanoes as information became available; these have been organized by month for convenience. Later publications were done in a monthly newsletter format. Links go to the profile page for each volcano with the Bulletin tab open.

Information is preliminary at time of publication and subject to change.

Yasur

Vanuatu

19.532°S, 169.447°E; summit elev. 361 m

All times are local (unless otherwise noted)

Strombolian activity continues during June 2019 through February 2020

Yasur has remained on Alert Level 2 (on a scale of 0-4) since 18 October 2016, indicating "Major Unrest; Danger Zone remains at 395 m around the eruptive vents." The summit crater contains several active vents that frequently produce Strombolian explosions and gas plumes (figure 60). This bulletin summarizes activity during June 2019 through February 2020 and is based on reports by the Vanuatu Meteorology and Geo-Hazards Department (VMGD), visitor photographs and videos, and satellite data.

Figure 60. The crater of Yasur contains several active vents that produce gas emissions and Strombolian activity. Photo taken during 25-27 October 2019 by Justin Noonan, used with permission.

A VMGD report on 27 June described ongoing Strombolian explosions with major unrest confined to the crater. The 25 July report noted the continuation of Strombolian activity with some strong explosions, and a warning that volcanic bombs may impact outside of the crater area (figure 61).

Figure 61. A volcanic bomb (a fluid chunk of lava greater than 64 mm in diameter) that was ejected from Yasur. The pattern on the surface shows the fluid nature of the lava before it cooled into a solid rock. Photo taken during 25-27 October 2019 by Justin Noonan, used with permission.

No VMGD report was available for August, but Strombolian activity continued with gas emissions and explosions, as documented by visitors (figure 62). The eruption continued through September and October with some strong explosions and multiple active vents visible in thermal satellite imagery (figure 63). Strombolian explosions ejecting fluid lava from rapidly expanding gas bubbles were recorded during October, and likely represented the typical activity during the surrounding months (figure 64). Along with vigorous degassing producing a persistent plume there was occasional ash content (figure 65). At some point during 20-29 October a small landslide occurred along the eastern inner wall of the crater, visible in satellite images and later confirmed to have produced ashfall at the summit (figure 66).

Figure 62. Different views of the Yasur vents on 7-8 August 2019 taken from a video. Strombolian activity and degassing were visible. Courtesy of Arnold Binas, used with permission.

Figure 64. Strombolian explosions at Yasur during 25-27 October 2019. Large gas bubbles rise to the top of the lava column and burst, ejecting volcanic bombs – fluid chunks of lava, out of the vent. Photos by Justin Noonan, used with permission.

Figure 65. Gas and ash emissions rise from the active vents at Yasur between 25-27 October 2019. Photos by Justin Noonan, used with permission.

Figure 66. Planet Scope satellite images of Yasur show a change in the crater morphology between 20 and 29 October 2019. Copyright of Planet Labs.

Continuous explosive activity continued in November-February with some stronger explosions recorded along with accompanying gas emissions. Gas plumes of sulfur dioxide were detected by satellite sensors on some days through this period (figure 67) and ash content was present at times (figure 68). Thermal anomalies continued to be detected by satellite sensors with varying intensity, and with a reduction in intensity in February, as seen in Sentinel-2 imagery and the MIROVA system (figures 69 and 70).

Figure 67. SO2 plumes detected at Yasur by Aura/OMI on 21 December 2019 and 31 January 2020, drifting W to NW, and on 14 and 23 February 2020, drifting W and south, and NWW to NW. Courtesy of Global Sulfur Dioxide Monitoring Page, NASA.

Figure 68. An ash plume erupts from Yasur on 20 February 2020 and drifts NW. Courtesy of Planet Labs.

Figure 70. The MIROVA thermal detection system recorded persistent thermal energy emitted at Yasur with some variation from mid-May 2019 to May 2020. There was a reduction in detected energy after January. Courtesy of MIROVA.

Geologic Background. Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has been in more-or-less continuous Strombolian and Vulcanian activity since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island, this mostly unvegetated pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide, horseshoe-shaped caldera associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

Cleveland

United States

52.825°N, 169.944°W; summit elev. 1730 m

All times are local (unless otherwise noted)

Cleveland is a stratovolcano located in the western portion of Chuginadak Island, a remote island part of the east central Aleutians. Common volcanism has included small lava flows, explosions, and ash clouds. Intermittent lava dome growth, small ash explosions, and thermal anomalies have characterized more recent activity (BGVN 44:02). For this reporting period during February 2019-January 2020, activity largely consisted of gas-and-steam emissions and intermittent thermal anomalies within the summit crater. The primary source of information comes from the Alaska Volcano Observatory (AVO) and various satellite data.

Low levels of unrest occurred intermittently throughout this reporting period with gas-and-steam emissions and thermal anomalies as the dominant type of activity (figures 30 and 31). An explosion on 9 January 2019 was followed by lava dome growth observed during 12-16 January. Suomi NPP/VIIRS sensor data showed two hotspots on 8 and 14 February 2019, though there was no evidence of lava within the summit crater at that time. According to satellite imagery from AVO, the lava dome was slowly subsiding during February into early March. Elevated surface temperatures were detected on 17 and 24 March in conjunction with degassing; another gas-and-steam plume was observed rising from the summit on 30 March. Thermal anomalies were again seen on 15 and 28 April using Suomi NPP/VIIRS sensor data. Intermittent gas-and-steam emissions continued as the number of detected thermal anomalies slightly increased during the next month, occurring on 1, 7, 15, 18, and 23 May. A gas-and-steam plume was observed on 9 May.

Figure 30. The MIROVA graph of thermal activity (log radiative power) at Cleveland during 4 February 2019 through January 2020 shows increased thermal anomalies between mid-April to late November 2019. Courtesy of MIROVA.

Figure 31. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed intermittent thermal signatures occurring in the summit crater during March 2019 through October 2019. Some gas-and-steam plumes were observed accompanying the thermal anomaly, as seen on 17 March 2019 and 8 May 2019. Courtesy of Sentinel Hub Playground.

There were 10 thermal anomalies observed in June, and 11 each in July and August. Typical mild degassing was visible when photographed on 9 August (figure 32). On 14 August, seismicity increased, which included a swarm of a dozen local earthquakes. The lava dome emplaced in January was clearly visible in satellite imagery (figure 33). The number of thermal anomalies decreased the next month, occurring on 10, 21, and 25 September. During this month, a gas-and-steam plume was observed in a webcam image on 6, 8, 20, and 25 September. On 3-6, 10, and 21 October elevated surface temperatures were recorded as well as small gas-and-steam plumes on 4, 7, 13, and 20-25 October.

Figure 32. Photograph of Cleveland showing mild degassing from the summit vent taken on 9 August 2019. Photo by Max Kaufman; courtesy of AVO/USGS.

Figure 33. Satellite image of Cleveland showing faint gas-and-steam emissions rising from the summit crater. High-resolution image taken on 17 August 2019 showing the lava dome from January 2019 inside the crater (dark ring). Image created by Hannah Dietterich; courtesy of AVO/USGS and DigitalGlobe.

Four thermal anomalies were detected on 3, 6, and 8-9 November. According to a VONA report from AVO on 8 November, satellite data suggested possible slow lava effusion in the summit crater; however, by the 15th no evidence of eruptive activity had been seen in any data sources. Another thermal anomaly was observed on 14 January 2020. Gas-and-steam emissions observed in webcam images continued intermittently.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows intermittent weak thermal anomalies within 5 km of the crater summit during mid-April through November 2019 with a larger cluster of activity in early June, late July and early October (figure 30). Thermal satellite imagery from Sentinel-2 also detected weak thermal anomalies within the summit crater throughout the reporting period, occasionally accompanied by gas-and-steam plumes (figure 31).

Geologic Background. The beautifully symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle volcano and NE across Chuginadak Pass strait from Herbert volcano. Joined to the rest of Chuginadak Island by a low isthmus, Cleveland is the highest of the Islands of the Four Mountains group and is one of the most active of the Aleutian Islands. The native name, Chuginadak, refers to the Aleut goddess of fire, who was thought to reside on the volcano. Numerous large lava flows descend the steep-sided flanks. It is possible that some 18th-to-19th century eruptions attributed to Carlisle should be ascribed to Cleveland (Miller et al., 1998). In 1944 Cleveland produced the only known fatality from an Aleutian eruption. Recent eruptions have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks.

San Miguel

El Salvador

13.434°N, 88.269°W; summit elev. 2130 m

All times are local (unless otherwise noted)

Small ash emissions during 22 February 2020

San Miguel, locally known as Chaparrastique, is a stratovolcano located in El Salvador. Recent activity has consisted of occasional small ash explosions and ash emissions. Infrequent gas-and-steam and ash emissions were observed during this reporting period of June 2018-March 2020. The primary source of information for this report comes from El Salvador's Servicio Nacional de Estudios Territoriales (SNET) and special reports from the Ministero de Medio Ambiente y Recursos Naturales (MARN) in addition to various satellite data.

Based on Sentinel-2 satellite imagery and analyses of infrared MODIS data, volcanism at San Miguel from June 2018 to mid-February was relatively low, consisting of occasional gas-and-steam emissions. During 2019, a weak thermal anomaly in the summit crater was registered in thermal satellite imagery (figure 27). This thermal anomaly persisted during a majority of the year but was not visible after September 2019; faint gas-and-steam emissions could sometimes be seen rising from the summit crater.

Volcanism was prominent beginning on 13-20 February 2020 when SO2 emissions exceeded 620 tons/day (typical low SO2 values are less than 400 tons/day). During 20-21 February the amplitude of microearthquakes increased and minor emissions of gas-and-steam and SO2 were visible within the crater (figure 28). According to SNET and special reports from MARN, on 22 February at 1055 an ash cloud was visible rising 400 m above the crater rim (figure 29), resulting in minor ashfall in Piedra Azul (5 km SW). That same day RSAM values peaked at 550 units as recorded by the VSM station on the upper N flank, which is above normal values of about 150. Seismicity increased the day after the eruptive activity. Minor gas-and-steam emissions continued to rise 400 m above the crater rim during 23-24 February; the RSAM values fell to 33-97 units. Activity in March was relatively low; some seismicity, including small magnitude earthquakes, occurred during the month in addition to SO2 emissions ranging from 517 to 808 tons/day.

Figure 28. Minor gas-and-steam emissions rising from the crater at San Miguel on 21 February 2020. Courtesy of Ministero de Medio Ambiente y Recursos Naturales (MARN).

Figure 29. Gas-and-steam and ash emissions rising from the crater at San Miguel on 22 February 2020. Courtesy of Ministero de Medio Ambiente y Recursos Naturales (MARN).

Geologic Background. The symmetrical cone of San Miguel volcano, one of the most active in El Salvador, rises from near sea level to form one of the country's most prominent landmarks. The unvegetated summit rises above slopes draped with coffee plantations. A broad, deep crater complex that has been frequently modified by historical eruptions (recorded since the early 16th century) caps the truncated summit, also known locally as Chaparrastique. Radial fissures on the flanks of the basaltic-andesitic volcano have fed a series of historical lava flows, including several erupted during the 17th-19th centuries that reached beyond the base of the volcano on the N, NE, and SE sides. The SE-flank flows are the largest and form broad, sparsely vegetated lava fields crossed by highways and a railroad skirting the base of the volcano. The location of flank vents has migrated higher on the edifice during historical time, and the most recent activity has consisted of minor ash eruptions from the summit crater.

Ambrym

Vanuatu

16.25°S, 168.12°E; summit elev. 1334 m

All times are local (unless otherwise noted)

Ambrym is an active volcanic island in the Vanuatu archipelago consisting of a 12 km-wide summit caldera. Benbow and Marum are two currently active craters within the caldera that have produced lava lakes, explosions, lava flows, ash, and gas emissions, in addition to fissure eruptions. More recently, a submarine fissure eruption in December 2018 produced lava fountains and lava flows, which resulted in the drainage of the active lava lakes in both the Benbow and Marum craters (BGVN 44:01). This report updates information from January 2019 through March 2020, including the submarine pumice eruption during December 2018 using information from the Vanuatu Meteorology and Geohazards Department (VMGD) and research by Shreve et al. (2019).

Activity on 14 December 2018 consisted of thermal anomalies located in the lava lake that disappeared over a 12-hour time period; a helicopter flight on 16 December confirmed the drainage of the summit lava lakes as well as a partial collapse of the Benbow and Marum craters (figure 49). During 14-15 December, a lava flow (figure 49), accompanied by lava fountaining, was observed originating from the SE flank of Marum, producing SO2 and ash emissions. A Mw 5.6 earthquake on 15 December at 2021 marked the beginning of a dike intrusion into the SE rift zone as well as a sharp increase in seismicity (Shreve et al., 2019). This intrusion extended more than 30 km from within the caldera to beyond the east coast, with a total volume of 419-532 x 106 m3 of magma. More than 2 m of coastal uplift was observed along the SE coast due to the asymmetry of the dike from December, resulting in onshore fractures.

Figure 49. Sentinel-2 thermal satellite images of Ambrym before the December 2018 eruption (left), and during the eruption (right). Before the eruption, the thermal signatures within both summit craters were strong and after the eruption, the thermal signatures were no longer detected. A lava flow was observed during the eruption on 15 December. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

Shreve et al. (2019) state that although the dike almost reached the surface, magma did not erupt from the onshore fractures; only minor gas emissions were detected until 17 December. An abrupt decrease in the seismic moment release on 17 December at 1600 marked the end of the dike propagation (figure 50). InSAR-derived models suggested an offshore eruption (Shreve et al., 2019). This was confirmed on 18-19 December when basaltic pumice, indicating a subaqueous eruption, was collected on the beach near Pamal and Ulei. Though the depth and exact location of the fissure has not been mapped, the nature of the basaltic pumice would suggest it was a relatively shallow offshore eruption, according to Shreve et al. (2019).

Figure 50. Geographical timeline summary of the December 2018 eruptive events at Ambrym. The lava lake level began to drop on 14 December, with fissure-fed lava flows during 14-15 December. After an earthquake on 15 December, a dike was detected, causing coastal uplift as it moved E. As the dike continued to propagate upwards, faulting was observed, though magma did not breach the surface. Eventually a submarine fissure eruption was confirmed offshore on 18-19 December. Image modified from Shreve et al. (2019).

In the weeks following the dike emplacement, there was more than 2 m of subsidence measured at both summit craters identified using ALOS-2 and Sentinel-1 InSAR data. After 22 December, no additional large-scale deformation was observed, though a localized discontinuity (less than 12 cm) measured across the fractures along the SE coast in addition to seismicity suggested a continuation of the distal submarine eruption into late 2019. Additional pumice was observed on 3 February 2019 near Pamal village, suggesting possible ongoing activity. These surveys also noted that no gas-and-steam emissions, lava flows, or volcanic gases were emitted from the recently active cracks and faults on the SE cost of Ambrym.

During February-October 2019, onshore activity at Ambrym declined to low levels of unrest, according to VMGD. The only activity within the summit caldera consisted of gas-and-steam emissions, with no evidence of the previous lava lakes (figure 51). Intermittent seismicity and gas-and-steam emissions continued to be observed at Ambrym and offshore of the SE coast. Mével et al. (2019) installed three Trillium Compact 120s posthole seismometers in the S and E part of Ambrym from 25 May to 5 June 2019. They found that there were multiple seismic events, including a Deep-Long Period event and mixed up/down first motions at two stations near the tip of the dike intrusion and offshore of Pamal at depths of 15-20 km below sea level. Based on a preliminary analysis of these data, Mével et al. (2019) interpreted the observations as indicative of ongoing volcanic seismicity in the region of the offshore dike intrusion and eruption.

Seismicity was no longer reported from 10 October 2019 through March 2020. Thermal anomalies were not detected in satellite data except for one in late April and one in early September 2019, according to MODIS thermal infrared data analyzed by the MIROVA system. The most recent report from VMGD was issued on 27 March 2020, which noted low-level unrest consisting of dominantly gas-and-steam emissions.

Geologic Background. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides Arc. A thick, almost exclusively pyroclastic sequence, initially dacitic then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major Plinian eruption with dacitic pyroclastic flows about 1,900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

Copahue

Chile-Argentina

37.856°S, 71.183°W; summit elev. 2953 m

All times are local (unless otherwise noted)

Ash emissions end on 12 November; lake returns to El Agrio Crater in December 2019

Most of the large edifice of Copahue lies high in the central Chilean Andes, but the active El Agrio crater lies on the Argentinian side of the border at the W edge of the Pliocene Caviahue caldera. Infrequent mild-to-moderate explosive eruptions have been recorded since the 18th century. The most recent eruptive episode began with phreatic explosions and ash emissions on 2 August 2019 that continued until mid-November 2019. This report summarizes activity from November 2019 through February 2020 and is based on reports issued by Servicio Nacional de Geología y Minería (SERNAGEOMIN) Observatorio Volcanológico de Los Andes del Sur (OVDAS), Buenos Aires Volcanic Ash Advisory Center (VAAC), satellite data, and photographs from nearby residents.

MIROVA data indicated a few weak thermal anomalies during mid-October to mid-November 2019. Multiple continuous ash emissions were reported daily until mid-November when activity declined significantly. By mid-December the lake inside El Agrio crater had reappeared and occasional steam plumes were the only reported surface activity at Copahue through February 2020.

The Buenos Aires VAAC and SERNAGEOMIN both reported continuous ash emissions during 1-9 November 2019 that were visible in the webcam. Satellite imagery recorded the plumes drifting generally E or NE at 3.0-4.3 km altitude (figure 49). Most of the emissions on 10 November were steam (figure 50). The last pulse of ash emissions occurred on 12 November with an ash plume visible moving SE at 3 km altitude in satellite imagery and a strong thermal anomaly (figure 51). The following day emissions were primarily steam and gas. SERNAGEOMIN noted the ash emissions rising around 800 m above El Agrio crater and also reported incandescence visible during most nights through mid-November. During the second half of November the constant degassing was primarily water vapor with occasional nighttime incandescence. Steam plumes rose 450 m above the crater on 27 November.

Figure 50. Most of the emissions from Copahue on 10 November 2019 were steam. Left image courtesy of Valentina Sepulveda, taken from Caviahue, Argentina. Right image courtesy of Sentinel Hub Playground, natural color rendering using bands 4, 3, and 2.

Nighttime incandescence was last observed in the SERNAGEOMIN webcam on 1 December; SERNAGEOMIN lowered the alert level from Yellow to Green on 15 December 2019. Throughout December degassing consisted mainly of minor steam plumes (figure 52), the highest plume rose to 300 m above the crater on 18 December, and minor SO2 plumes persisted through the 21st (figure 53),. By mid-December the El Agrio crater lake was returning and satellite images clearly showed the increase in size of the lake through February (figure 54). The only surface activity reported during January and February 2020 was occasional white steam plumes rising near El Agrio crater.

Figure 52. Small wisps of steam were the only emissions from Copahue on 3 December 2019. Courtesy of Valentina Sepulveda, taken from Caviahue, Argentina.

Figure 53. Small plumes of SO2 were recorded at Copahue during November and December 2019. Top row: 7, 9, and 30 November. Bottom row: 1, 20, and 21 December. Courtesy of Global Sulfur Dioxide Monitoring Page, NASA.

Figure 54. The lake within El Agrio crater reappeared between 5 and 12 December 2019 and continued to grow in size through the end of January 2020. Top row (left to right): There was no lake inside the crater on 5 December 2019, only a small steam plume rising from the vent. The first water was visible on 12 December and was slightly larger a few days later on 17 December. Bottom row (left to right): the lake was significantly larger on 4 January 2020 filling an embayment close to the steam vent. Fingers of water filled in areas of the crater as the water level rose on 24 and 29 January. Courtesy of Sentinel Hub Playground.

Geologic Background. Volcán Copahue is an elongated composite cone constructed along the Chile-Argentina border within the 6.5 x 8.5 km wide Trapa-Trapa caldera that formed between 0.6 and 0.4 million years ago near the NW margin of the 20 x 15 km Pliocene Caviahue (Del Agrio) caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains a briny, acidic 300-m-wide crater lake (also referred to as El Agrio or Del Agrio) and displays intense fumarolic activity. Acidic hot springs occur below the eastern outlet of the crater lake, contributing to the acidity of the Río Agrio, and another geothermal zone is located within Caviahue caldera about 7 km NE of the summit. Infrequent mild-to-moderate explosive eruptions have been recorded since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.

Japan

27.247°N, 140.874°E; summit elev. 25 m

All times are local (unless otherwise noted)

After 40 years of dormancy, Japan’s Nishinoshima volcano, located about 1,000 km S of Tokyo in the Ogasawara Arc, erupted above sea level in November 2013. Lava flows were active through November 2015, emerging from a central pyroclastic cone. A new eruption in mid-2017 continued the growth of the island with ash plumes, ejecta, and lava flows. A short eruptive event in July 2018 produced a new lava flow and vent on the side of the pyroclastic cone. The next eruption of ash plumes, incandescent ejecta, and lava flows, covered in this report, began in early December 2019 and was ongoing through February 2020. Information is provided primarily from the Japan Meteorological Agency (JMA) monthly reports.

Nishinoshima remained quiet after a short eruptive event in July 2018 until MODVOLC thermal alerts appeared on 5 December 2019. Multiple near-daily alerts continued through February 2020. The intermittent low-level thermal anomalies seen in the MIROVA data beginning in May and June 2019 may reflect areas with increased temperatures and fumarolic activity reported by the Japan Coast Guard during overflights in June and July. The significant increase in thermal anomalies in the MIROVA data on 5 December correlates with the beginning of extrusive and explosive activity (figure 63). Eruptive activity included ash emissions, incandescent ejecta, and numerous lava flows from multiple vents that flowed into the sea down several flanks, significantly enlarging the island.

Figure 63. The MIROVA graph of thermal energy from Nishinoshima from 13 April 2019 through February 2020 shows low-level thermal activity beginning in mid-2019; there were reports of increased temperatures and fumarolic activity during that time. Eruptive activity including ash emissions, incandescent ejecta, and numerous lava flows began on 5 December 2019 and was ongoing through February 2020. Courtesy of MIROVA.

A brief period of activity during 12-21 July 2018 produced explosive activity with blocks and bombs ejected 500 m from a new vent on the E flank of the pyroclastic cone, and a 700-m-long lava flow that stopped about 100 m before reaching the ocean (BGVN 43:09). No further activity was reported during 2018. During overflights on 29 and 31 January, and 7 February 2019, white steam plumes drifted from the E crater margin and inner wall of the pyroclastic cone and discolored waters were present around the island, but no other signs of activity were reported. A survey carried out by the Japan Coast Guard during 7-8 June 2019 reported minor fumarolic activity from the summit crater, and high-temperature areas were noted on the hillsides, measured by infrared thermal imaging equipment. Sulfur dioxide emissions were below the detection limit. In an overflight on 12 July 2019, Coast Guard personnel noted a small white plume rising from the E edge of the summit crater of the pyroclastic cone (figure 64).

Figure 64. The Japan Coast Guard noted a small white plume at the summit of Nishinoshima during an overflight on 12 July 2019, but no other signs of activity. Courtesy of JMA (Volcanic activity monthly report, July 2019).

The white plume was still present during an overflight on 14 August 2019. Greenish yellow areas of water about 500 m wide were distributed around the island, and a plume of green water extended 1.8 km from the NW coast. Similar conditions were observed on 15 October 2019; pale yellow-green discolored water was about 100 m wide and concentrated on the N shore of Nishinoshima. No steam plume from the summit was present during a visit on 19 November 2019, but yellow-white discolored water on the N shore was about 100 m wide and 700 m long. Along the NE and SE coasts, yellow-white water was 100-200 m wide and about 1,000 m long.

A MODVOLC thermal alert appeared at Nishinoshima on 5 December 2019. An eruption was observed by the Japan Coast Guard the following day. A pulsating light gray ash plume rose from the summit crater accompanied by tephra ejected 200 m above the crater rim every few minutes (figure 65). In addition, ash and tephra rose intermittently from a crater on the E flank of the pyroclastic cone, from which lava also flowed down towards the E coast (figure 66). By 1300 on 7 December the lava was flowing into the sea (figure 67).

Figure 65. The eruption observed at Nishinoshima on 6 December 2019 included ash and tephra emissions from the summit vent, and ash, tephra, and a lava flow from the vent on the E flank of the pyroclastic cone. Courtesy of JMA (Volcanic activity monthly report, November 2019).

Figure 67. By 1300 on 7 December 2019 lava from the E-flank vent at Nishinoshima was flowing into the sea. Courtesy of JMA (Volcanic activity monthly report, November 2019).

Observations by the Japan Coast Guard on 15 December 2019 confirmed that vigorous eruptive activity was ongoing; incandescent ejecta and ash plumes rose 300 m above the summit crater rim (figure 68). A new vent had opened on the N flank of the cone from which lava flowed NW to the sea (figure 69). The lava flow from the E-flank crater also remained active and continued flowing into the sea. The Tokyo VAAC reported an ash emission on 24 December that rose to 1,000 m altitude and drifted S. On 31 December, explosions at the summit continued every few seconds with ash and ejecta rising 300 m high. In addition, lava from the NE flank of the pyroclastic cone flowed NE to the sea (figure 70).

Figure 69. Lava from a new vent on the NW flank of Nishinoshima was entering the sea on 15 December 2019, producing vigorous steam plumes. Courtesy of JMA (Volcanic activity monthly report, December 2019).

Figure 70. At Nishinoshima on 31 December 2019 lava flowed down the NE flank of the pyroclastic cone into the sea, and incandescent ejecta rose 300 m above summit. Courtesy of JMA and the Japan Coast Guard (Volcanic activity monthly report, December 2019).

Satellite data from JAXA (Japan Aerospace Exploration Agency) made it possible for JMA to produce maps showing the rapid changes in topography at Nishinoshima resulting from the new lava flows. The new E-flank lava flow was readily seen when comparing imagery from 22 November with 6 December 2019 (figure 71a). An image from 6 December compared with 20 December 2019 shows the flow on the E flank splitting and entering the sea at two locations (figure 71b), the flow on the NW flank traveling briefly N before turning W and forming a large fan into the ocean on the W flank, and a new flow heading NE from the summit area of the pyroclastic cone.

Figure 71. Satellite data from JAXA (Japan Aerospace Exploration Agency) made it possible to produce maps showing the changes in topography at Nishinoshima resulting from the new lava flows (shown in blue). In comparing 22 November with 6 December 2019 (A, left), the new lava flow on the E flank was visible. A new image from 20 December compared with 6 December (B, right) showed the flow on the E flank splitting and entering the sea at two locations, the NW-flank flow building a large fan into the ocean on the W flank, and a new flow heading NE from the summit area of the pyroclastic cone. Courtesy of JMA and the Japan Coast Guard (Volcanic activity monthly report, December 2019).

The Tokyo VAAC reported an ash plume visible in satellite imagery on 15 January 2020 that rose to 1.8 km altitude and drifted SE. The Japan Coast Guard conducted an overflight on 17 January that confirmed the continued eruptions of ash, incandescent ejecta, and lava. Dark gray ash plumes were observed at 1.8 km altitude, with ashfall and tephra concentrated around the pyroclastic cone (figure 72). Plumes of steam were visible where the NE lava flow entered the ocean; the E and NW lava entry areas did not appear active but were still hot. Satellite data from ALOS-2 prepared by JAXA confirmed ongoing activity around the summit vent and on the NE flank, while activity on the W flank had ceased (figure 73). An ash plume was reported by the Tokyo VAAC on 25 January; it rose to 1.5 km altitude and drifted SW for most of the day.

Figure 72. Dense, dark gray ash plumes rose from the summit of Nishinoshima on 17 January 2020. Small plumes of steam from lava-seawater interactions were visible on the NE shore of the island as well (far right). Courtesy of JMA and the Japan Coast Guard (Volcanic activity monthly report, January 2020).

Figure 73. JAXA satellite data from 3 January 2020 (left) showed the growth of a new lava delta on the NE flank of Nishinoshima and minor activity occuring on the W flank compared with the previous image from 20 December 2019. By 17 January 2020 (right), the lava flow activity was concentrated on the NE flank with multiple deltas extending out into the sea. The ‘low correlation areas’ shown in blue represent changes in topography caused by new material from lava flows and ejecta added between the dates shown above the images. Courtesy of JMA (Volcanic activity monthly report, January 2020).

On 3 Feburary 2020 the Tokyo VAAC reported an ash plume visible in satellite imagery that rose to 2.1 km altitude and drifted E. The following day the Japan Coast Guard observed eruptions from the summit crater at five minute intervals that produced grayish white plumes. The plumes rose to 2.7 km altitude (figure 74). Large bombs were scattered around the pyroclastic cone, and the summit crater appeared filled with lava except for the active vent. The lava deltas on the NE flank were only active at the tips of the flows producing a few steam jets where lava entered the sea. The active flows were on the SE flank, and a new 200-m-long lava flow was flowing down the N flank of the pyroclastic cone (figure 75). The lava flowing from the E flank of the pyroclastic cone to the SE into the sea, produced larger jets of steam (figure 76). Yellow-brown discolored water appeared around the island in several places.

Figure 74. Ash emissions at Nishinoshima rose to 2.7 km altitude on 4 February 2020; steam jets from lava entering the ocean were active on the SE flank (far side of the island, right). Courtesy of JMA (Volcanic activity monthly report, February 2020).

Figure 75. The lava deltas on the NE flank of Nishinoshima (bottom center) were much less active on 4 February 2020 than the lava flow and growing delta on the SE flank (left). The newest flow headed N from the summit and was 200 m long (right of center). Courtesy of JMA and the Japan Coast Guard (Volcanic activity monthly report, February 2020).

Figure 76. The most active lava flows at Nishinoshima on 4 February 2020 were on the E flank; significant steam plumes rose in multiple locations along the coast where they entered the sea. Intermittent ash plumes also rose from the summit crater. Courtesy of JMA and Japan Coast Guard (Volcanic activity monthly report, February 2020).

JAXA satellite data confirmed that the flow activity was concentrated on the NE flank and shore during the second half of January 2020, but also recorded the new flow down the SE flank that was observed by the Coast Guard in early February. By mid-February the satellite topographic data indicated the decrease in activity in the NE flank flows, the increased activity on the SE and E flank, and the extension of the flow moving due N to the coast (figure 77). Observations on 17 February 2020 by the Japan Coast Guard revealed eruptions from the summit crater every few seconds, and steam-and-ash plumes rising about 600 m. Vigorous white emissions rose from fractures near the top of the W flank of the pyroclastic cone, but thermal data indicated the area was no hotter than the surrounding area (figure 78). The lava flow on the SE coast still had steam emissions rising from the ocean entry point, but activity was weaker than on 4 February. The newest flow moving due N from the summit produced steam emissions where the flow front entered the ocean.

Figure 77. Constantly changing lava flows at Nishinoshima reshaped the island during late January and February 2020. During the second half of January, flows were active on the NE flank, creating deltas into the sea off the NE coast and also on the SE flank into the sea at the SE coast (left). The ‘low correlation areas’ shown in blue represent changes in topography caused by new material from lava flows and ejecta added between the dates shown above the images. By 14 February (right) activity had slowed on the NE flank and expanded on the SE flank and N flank. Data is from the Land Observing Satellite-2 "Daichi-2" (ALOS-2). Courtesy of JMA and JAXA (Volcanic activity monthly report, February 2020).

Figure 78. Vigorous white emissions rose from fractures near the top of the W flank of the pyroclastic cone at Nishinoshima on 17 February 2020, but thermal data indicated the area was no hotter than the surrounding area. Courtesy of JMA and Japan Coast Guard (Volcanic activity monthly report, February 2020).

Sulfur dioxide plumes from Nishinoshima have been small and infrequent in recent years, but the renewed and increased eruptive activity beginning in December 2019 produced several small SO2 plumes that were recorded in daily satellite data (figure 79).

Figure 79. Small sulfur dioxide plumes from Nishinoshima were captured by the TROPOMI instrument on the Sentinel 5P satellite a few times during December 2019-February 2020 as the eruptive activity increased. The large red streak in the 3 February 2020 image is SO2 from an eruption of Kuchinoerabujima volcano (Ryukyu Islands) on the same day. Courtesy of NASA Goddard Space Flight Center and Simon Carn.

Geologic Background. The small island of Nishinoshima was enlarged when several new islands coalesced during an eruption in 1973-74. Another eruption that began offshore in 2013 completely covered the previous exposed surface and enlarged the island again. Water discoloration has been observed on several occasions since. The island is the summit of a massive submarine volcano that has prominent satellitic peaks to the S, W, and NE. The summit of the southern cone rises to within 214 m of the sea surface 9 km SSE.

Krakatau

Indonesia

6.102°S, 105.423°E; summit elev. 155 m

All times are local (unless otherwise noted)

Tephra and steam explosions in the crater lake; explosions in December 2019 build a tephra cone

Krakatau volcano in the Sunda Strait between Indonesia’s Java and Sumatra Islands experienced a major caldera collapse around 535 CE; it formed a 7-km-wide caldera ringed by three islands. Remnants of this volcano joined to create the pre-1883 Krakatau Island which collapsed during the major 1883 eruption. Anak Krakatau (Child of Krakatau), constructed beginning in late 1927 within the 1883 caldera (BGVN 44:03, figure 56), was the site of over 40 eruptive episodes until 22 December 2018 when a large explosion and flank collapse destroyed most of the 338-m-high edifice and generated a deadly tsunami (BGVN 44:03). The near-sea level crater lake inside the remnant of Anak Krakatau was the site of numerous small steam and tephra explosions from February (BGVN 44:08) through November 2019. A larger explosion in December 2019 produced the beginnings of a new cone above the surface of crater lake. Activity from August 2019 through January 2020 is covered in this report with information provided by the Indonesian Center for Volcanology and Geological Hazard Mitigation, referred to as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG). Aviation reports are provided by the Darwin Volcanic Ash Advisory Center (VAAC), and photographs are from the PVMBG webcam and visitors to the island.

Explosions were reported on more than ten days each month from August to October 2019. They were recorded based on seismicity, but webcam images also showed black tephra and steam being ejected from the crater lake to heights up to 450 m. Activity decreased significantly after the middle of November, although smaller explosions were witnessed by visitors to the island. After a period of relative quiet, a larger series of explosions at the end of December produced ash plumes that rose up to 3 km above the crater; the crater lake was largely filled with tephra after these explosions. Thermal activity persisted throughout the period of August 2019-January 2020. The wattage of Radiative Power increased from August through mid-October, and then decreased through January 2020 (figure 96).

Figure 96. Thermal activity persisted at Anak Krakatau from 20 March 2019-January 2020. The wattage of Radiative Power increased from August through mid-October, and then decreased through January 2020. Courtesy of MIROVA.

Activity during August-November 2019. The new profile of Anak Krakatau rose to about 155 m elevation as of August 2019, almost 100 m less than prior to the December 2018 explosions and flank collapse (figure 97). Smaller explosions continued during August 2019 and were reported by PVMBG in 12 different VONAs (Volcano Observatory Notice to Aviation) on days 1, 3, 6, 17, 19, 22, 23, 25, and 28. Most of the explosions lasted for less than two minutes, according to the seismic data. PVMBG reported steam plumes of 25-50 m height above the sea-level crater on 20 and 21 August. They reported a visible ash cloud on 22 August; it rose to an altitude of 457 m and drifted NNE according to the VONA. In their daily update, they noted that the eruption plume of 250-400 m on 22 August was white, gray, and black. The Darwin VAAC reported that the ash plume was discernable on HIMAWARI-8 satellite imagery for a short period of time. PVMBG noted ten eruptions on 24 August with white, gray, and black ejecta rising 100-300 m. A webcam installed at month’s end provided evidence of diffuse steam plumes rising 25-150 m above the crater during 28-31 August.

Figure 97. Only one tree survived on the once tree-covered spit off the NE end of Sertung Island after the December 2018 tsunami from Anak Krakatau covered it with ash and debris. The elevation of Anak Krakatau (center) was about 155 m on 8 August 2019, almost 100 m less than before the explosions and flank collapse. Panjang Island is on the left, and 746-m-high Rakata, the remnant of the 1883 volcanic island, is behind Anak Krakatau on the right. Courtesy of Amber Madden-Nadeau.

VONAs were issued for explosions on 1-3, 11, 13, 17, 18, 21, 24-27 and 29 September 2019. The explosion on 2 September produced a steam plume that rose 350 m, and dense black ash and ejecta which rose 200 m from the crater and drifted N. Gray and white tephra and steam rose 450 m on 13 and 17 September; ejecta was black and gray and rose 200 m on 21 September (figure 98). During 24-27 and 29 September tephra rose at least 200 m each day; some days it was mostly white with gray, other days it was primarily gray and black. All of the ejecta plumes drifted N. On days without explosions, the webcam recorded steam plumes rising 50-150 m above the crater.

Figure 98. Explosions of steam and dark ejecta were captured by the webcam on Anak Krakatau on 21 (left) and 26 (right) September 2019. Courtesy of MAGMA Indonesia and PVMBG.

Explosions were reported daily during 12-14, 16-20, 25-27, and 29 October (figure 99). PVMBG reported eight explosions on 19 October and seven explosions the next day. Most explosions produced gray and black tephra that rose 200 m from the crater and drifted N. On many of the days an ash plume also rose 350 m from the crater and drifted N. The seismic events that accompanied the explosions varied in duration from 45 to 1,232 seconds (about 20 minutes). The Darwin VAAC reported the 12 October eruption as visible briefly in satellite imagery before dissipating near the volcano. The first of four explosions on 26 October also appeared in visible satellite imagery moving NNW for a short time. The webcam recorded diffuse steam plumes rising 25-150 m above the crater on most days during the month.

Figure 99. A number of explosions at Anak Krakatau were captured by the webcam and visitors near the island during October 2019, shown here on the 12th, 14th, 17th, and 29th. Black and gray ejecta and steam plumes jetted several hundred meters high from the crater lake during the explosions. Webcam images courtesy of PVMBG and MAGMA Indonesia, with 12 October 2019 (top left) via VolcanoYT. Bottom left photo on 17 October courtesy of Christoph Sator.

Five VONAs were issued for explosions during 5-7 November, and one on 13 November 2019. The three explosions on 5 November produced 200-m-high plumes of steam and gray and black ejecta and ash plumes that rose 200, 450, and 550 m respectively; they all drifted N (figure 100). The Darwin VAAC reported ash drifting N in visible imagery for a brief period also. A 350-m-high ash plume accompanied 200-m-high ejecta on 6 November. Tephra rose 150-300 m from the crater during a 43 second explosion on 7 November. The explosion reported by PVMBG on 13 November produced black tephra and white steam 200 m high that drifted N. For the remainder of the month, when not obscured by fog, steam plumes rose daily 25-150 m from the crater.

Figure 100. PVMBG’s KAWAH webcam captured an explosion with steam and dark ejecta from the crater lake at Anak Krakatau on 5 November 2019. Courtesy of PVMBG and MAGMA Indonesia.

A joint expedition with PVMBG and the Earth Observatory of Singapore (EOS) installed geophysical equipment on Anak Krakatau and Rakata during 12 and 13 November 2019 (figure 101). Visitors to the island during 19-23 and 22-24 November recorded the short-lived landscape and continuing small explosions of steam and black tephra from the crater lake (figures 102 and 103).

Figure 101. A joint expedition to Anak Krakatau with PVMBG and the Earth Observatory of Singapore (EOS) installed geophysical equipment on Anak Krakatau and Rakata (background, left) during 12 and 13 November 2019. Images of the crater lake from the same spot (left) in December and January show the changes at the island (figure 108). Monitoring equipment installed near the shore sits over the many layers of ash and tephra that make up the island (right). Courtesy of Anna Perttu.

Figure 102.The crater lake at Anak Krakatau during a 19-23 November 2019 visit was the site of continued explosions with jets of steam and tephra that rose as high as 30 m. Courtesy of Andrey Nikiforov and Volcano Discovery, used with permission.

Figure 103. The landscape of Anak Krakatau recorded the rapidly evolving sequence of volcanic events during November 2019. Fresh ash covered recent lava near the shoreline on 22 November 2019 (top left). Large blocks of gray tephra (composed of other tephra fragments) were surrounded by reddish brown smaller fragments in the area between the crater and the ocean on 23 November 2019 (top right). Explosions of steam and black tephra rose tens of meters from the crater lake on 23 November 2019 (bottom). Courtesy of and copyright by Pascal Blondé.

Activity during December 2019-January 2020. Very little activity was recorded for most of December 2019. The webcam captured daily images of diffuse steam plumes rising 25-50 m above the crater which occasionally rose to 150 m. A new explosion on 28 December produced black and gray ejecta 200 m high that drifted N; the explosion was similar to those reported during August-November. A new series of explosions from 30 December 2019 to 1 January 2020 produced ash plumes which rose significantly higher than the previous explosions, reaching 2.4-3.0 km altitude and drifting S, E, and SE according to PVMBG (figure 104). They were initially visible in satellite imagery and reported drifting SW by the Darwin VAAC. By 31 December meteorological clouds prevented observation of the ash plume but a hotspot remained visible for part of that day.

Figure 104.The KAWAH webcam at Anak Krakatau captured this image of incandescent ejecta exploding from the crater lake on 30 December 2019 near the start of a new sequence of large explosions. Courtesy of PVMBG and Alex Bogár.

The explosions on 30 and 31 December 2019 were captured in satellite imagery (figure 105) and appeared to indicate that the crater lake was largely destroyed and filled with tephra from a new growing cone, according to Simon Carn. This was confirmed in both satellite imagery and ground-based photography in early January (figures 106 and 107).

Figure 105. Satellite imagery of the explosions at Anak Krakatau on 30 and 31 December 2019 showed dense steam rising from the crater (left) and a thermal anomaly visible through moderate cloud cover (right). Left image courtesy of Simon Carn, and copyright by Planet Labs, Inc. Right image uses Atmospheric Penetration rendering (bands 12, 11, and 8a) to show the thermal anomaly at the base of the steam plume, courtesy of Sentinel Hub Playground.

Figure 106. Sentinel-2 images of Anak Krakatau before (left, 21 December 2019) and after (right, 13 January 2020) explosions on 30 and 31 December 2019 show the filling in of the crater lake with new volcanic material. Natural color rendering based on bands 4,3, and 2. Courtesy of Sentinel Hub Playground.

Figure 107. The crater lake at Anak Krakatau changed significantly between the first week of December 2019 (left) and 8 January 2020 (right) after explosions on 30 and 31 December 2019. Compare with figure 101, taken from the same location in mid-November 2019. Left image courtesy of Piotr Smieszek. Right image courtesy of Peter Rendezvous.

Steam plumes rose 50-200 m above the crater during the first week of January 2020. An explosion on 7 January produced dense gray ash that rose 200 m from the crater and drifted E. Steam plume heights varied during the second week, with some plumes reaching 300 m above the crater. Multiple explosions on 15 January produced dense, gray and black ejecta that rose 150 m. Fog obscured the crater for most of the second half of the month; for a brief period, diffuse steam plumes were observed 25-1,000 m above the crater.

Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Mayotte

France

12.83°S, 45.17°E; summit elev. 660 m

All times are local (unless otherwise noted)

Seismicity and deformation, with submarine E-flank volcanism starting in July 2018

Mayotte is a volcanic island in the Comoros archipelago between the eastern coast of Africa and the northern tip of Madagascar. A chain of basaltic volcanism began 10-20 million years ago and migrating W, making up four principal volcanic islands, according to the Institut de Physique du Globe de Paris (IPGP) and Cesca et al. (2020). Before May 2010, only two seismic events had been felt by the nearby community within recent decades. New activity since May 2018 consists of dominantly seismic events and lava effusion. The primary source of information for this report through February 2020 comes from semi-monthly reports from the Réseau de Surveillance Volcanologique et Sismologique de Mayotte (REVOSIMA), a cooperative program between the Institut de Physique du Globe de Paris (IPGP), the Bureau de Recherches Géologiques et Minières (BRGM), and the Observatoire Volcanologique du Piton de la Fournaise (OVPF-IPGP); Lemoine et al. (2019), the Centre National de la Recherche Scientifique (CNRS), and the Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER).

Seismicity was the dominant type of activity recorded in association with a new submarine eruption. On 10 May 2018, the first seismic event occurred at 0814, detected by the YTMZ accelerometer from the French RAP Network, according to BRGM and Lemoine et al. (2019). Seismicity continued to increase during 13-15 May 2018, with the strongest recorded event for the Comoros area occurring on 15 May at 1848 and two more events on 20-21 May (figure 1). At the time, no surface effusion were directly observed; however, Global Navigation Satellite System (GNSS) instruments were deployed to monitor any ground motion (Lemoine et al. 2019).

Figure 1. A graph showing the number of daily seismic events greater than M 3.5 occurring offshore of Mayotte from 10 May 2018 through 15 February 2020. Seismicity significantly decreased in July 2018, but continued intermittently through February 2020, with relatively higher seismicity recorded in late August and mid-September 2018. Courtesy of IPGP and REVOSIMA.

Seismicity decreased dramatically after June 2018, with two spikes in August and September (see figure 1). Much of this seismicity occurred offshore 50 km E of Mayotte Island (figure 2). The École Normale Supérieure, the Observatoire Volcanologique du Piton de la Fournaise (OVPF-IPGP), and the REVOSIMA August 2019 bulletin reported that measurements from the GNSS stations and Teria GPS network data indicated eastward surface deformation and subsidence beginning in July 2018. Based on this ground deformation data Lemoine et al. (2019) determined that the eruptive phase began fifty days after the initial seismic events occurred, on 3 July 2018.

Figure 2. Maps of seismic activity offshore near Mayotte during May 2019. Seismic swarms occurred E of Mayotte Island (top) and continued in multiple phases through October 2019. New lava effusions were observed 50 km E of Petite Terre (bottom). Bottom image has been modified with annotations; courtesy of IPGP, BRGM, IFREMER, CNRS, and University of Paris.

Between 2 and 18 May 2019, an oceanographic campaign (MAYOBS 1) discovered a new submarine eruption site 50 km E from the island of Mayotte (figure 2). The director of IPGP, Marc Chaussidon, stated in an interview with Science Magazine that multibeam sonar waves were used to determine the elevation (800 m) and diameter (5 km) of the new submarine cone (figure 3). In addition, this multibeam sonar image showed fluid plumes within the water column rising from the center and flanks of the structure. According to REVOSIMA, these plumes rose to 1 km above the summit of the cone but did not breach the ocean surface. The seafloor image (figure 3) also indicated that as much as 5 km3 of magma erupted onto the seafloor from this new edifice during May 2019, according to Science Magazine.

Figure 3. Seafloor image of the submarine vent offshore of Mayotte created with multibeam sonar from 2 to 18 May 2019. The red line is the outline of the volcanic cone located at approximately 3.5 km depth. The blue-green color rising from the peak of the red outline represents fluid plumes within the water column. Courtesy of IPGP.

On 17 May 2019, a second oceanographic campaign (MAYOBS 2) discovered new lava flows located 5 km S of the new eruptive site. BRGM reported that in June a new lava flow had been identified on the W flank of the cone measuring 150 m thick with an estimated volume of 0.3 km3 (figure 4). According to REVOSIMA, the presence of multiple new lava flows would suggest multiple effusion points. Over a period of 11 months (July 2018-June 2019) the rate of lava effusion was at least 150-200 m3/s; between 18 May to 17 June 2019, 0.2 km3 of lava was produced, and from 17 June to 30 July 2019, 0.3 km3 of lava was produced. The MAYOBS 4 (19 July 2019-4 August 2019) and SHOM (20-21 August 2019) missions revealed a new lava flow formed between 31 July and 20 August to the NW of the eruptive site with a volume of 0.08 km3 and covering 3.25 km2.

Figure 4. Bathymetric map showing the location of the new lava flow on the W flank of the submarine cone offshore to the E of Mayotte Island. The MAYOBS 2 campaign was launched in June 2019 (left) and MAYOBS 4 was launched in late July 2019 (right). Courtesy of BRGM.

During the MAYOBS 4 campaign in late July 2019, scientists dredged the NE flank of the cone for samples and took photographs of the newly erupted lava (figure 5). Two dives found the presence of pillow lavas. When samples were brought up to the surface, they exploded due to the large amount of gas and rapid decompression.

Figure 5. Photographs taken using the submersible interactive camera system (SCAMPI) of newly formed pillow lavas (top) and a vesicular sample (bottom) dredged near the new submarine eruptive site at Mayotte in late July 2019. Courtesy of BRGM.

During April-May 2019 the rate of ground deformation slowed. Deflation was also observed up to 90 km E of Mayotte in late October 2019 and consistently between August 2019 and February 2020. Seismicity continued intermittently through February 2020 offshore E of Mayotte Island, though the number of detected events started to decrease in July 2018 (see figure 1). Though seismicity and deformation continued, the most recent observation of new lava flows occurred during the MAYOBS 4 and SHOM campaigns on 20 August 2019, as reported in REVOSIMA bulletins.

Geologic Background. Mayotte, located in the Mozambique Channel between the northern tip of Madagascar and the eastern coast of Africa, consists two main volcanic islands, Grande Terre and Petite Terre, and roughly twenty islets within a barrier-reef lagoon complex (Zinke et al., 2005; Pelleter et al., 2014). Volcanism began roughly 15-10 million years ago (Pelleter et al., 2014; Nougier et al., 1986), and has included basaltic lava flows, nephelinite, tephrite, phonolitic domes, and pyroclastic deposits (Nehlig et al., 2013). Lavas on the NE were active from about 4.7 to 1.4 million years and on the south from about 7.7 to 2.7 million years. Mafic activity resumed on the north from about 2.9 to 1.2 million years and on the south from about 2 to 1.5 million years. Several pumice layers found in cores on the barrier reef-lagoon complex indicate that volcanism likely occurred less than 7,000 years ago (Zinke et al., 2003). More recent activity that began in May 2018 consisted of seismicity and ground deformation occurring offshore E of Mayotte Island (Lemoine et al., 2019). One year later, in May 2019, a new subaqueous edifice and associated lava flows were observed 50 km E of Petite Terre during an oceanographic campaign.

Fernandina

Ecuador

0.37°S, 91.55°W; summit elev. 1476 m

All times are local (unless otherwise noted)

Fissure eruption produced lava flows during 12-13 January 2020

Fernandina is a volcanic island in the Galapagos islands, around 1,000 km W from the coast of mainland Ecuador. It has produced nearly 30 recorded eruptions since 1800, with the most recent events having occurred along radial or circumferential fissures around the summit crater. The most recent previous eruption, starting on 16 June 2018, lasted two days and produced lava flows from a radial fissure on the northern flank. Monitoring and scientific reports come from the Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN).

A report from IG-EPN on 12 January 2020 stated that there had been an increase in seismicity and deformation occurring during the previous weeks. On the day of the report, 11 seismic events had occurred, with the largest magnitude of 4.7 at a depth of 5 km. Shortly before 1810 that day a circumferential fissure formed below the eastern rim of the La Cumbre crater, at about 1.3-1.4 km elevation, and produced lava flows down the flank (figure 39). A rapid-onset seismic swarm reached maximum intensity at 1650 on 12 January (figure 40); a second increase in seismicity indicating the start of the eruption began around 70 minutes later (1800). A hotspot was observed in NOAA / CIMSS data between 1800 and 1810, and a gas plume rising up to 2 km above the fissure dispersed W to NW. The eruption lasted 9 hours, until about 0300 on 13 January.

Figure 39. Lava flows erupting from a circumferential fissure on the eastern flank of Fernandina on 12 January 2020. Photos courtesy of Parque Nacional Galápagos.

Figure 40. Graph showing the Root-Mean-Square (RMS) amplitude of the seismic signals from the FER-1 station at Fernandina on 12-13 January 2020. The graph shows the increase in seismicity leading to the eruption on the 12th (left star), a decrease in the seismicity, and then another increase during the event (right star). Courtesy of S. Hernandez, IG-EPN (Report on 13 January 2020).

A report issued at 1159 local time on 13 January 2020 described a rapid decrease in seismicity, gas emissions, and thermal anomalies, indicating a rapid decline in eruptive activity similar to previous events in 2017 and 2018. An overflight that day confirmed that the eruption had ended, after lava flows had extended around 500 m from the crater and covered an area of 3.8 km2 (figures 41 and 42). Seismicity continued on the 14th, with small volcano-tectonic (VT) earthquakes occurring less than 500 m below the surface. Periodic seismicity was recorded through 13-15 January, though there was an increase in seismicity during 17-22 January with deformation also detected (figure 43). No volcanic activity followed, and no additional gas or thermal anomalies were detected.

Figure 41. The lava flow extents at Fernandina of the previous two eruptions (4-7 September 2017 and 16-21 June 2018) and the 12-13 January 2020 eruption as detected by FIRMS thermal anomalies. Thermal data courtesy of NASA; figure prepared by F. Vásconez, IG-EPN (Report on 13 January 2020).

Figure 42. This fissure vent that formed on the E flank of Fernandina on 12 January 2020 produced several lava flows. A weak gas plume was still rising when this photo was taken the next day, but the eruption had ceased. Courtesy of Parque Nacional Galápagos.

Figure 43. Soil displacement map for Fernandina during 10 and 16 January 2020, with the deformation generated by the 12 January eruption shown. Courtesy of IG-EPN (Report on 23 January 2020).

Geologic Background. Fernandina, the most active of Galápagos volcanoes and the one closest to the Galápagos mantle plume, is a basaltic shield volcano with a deep 5 x 6.5 km summit caldera. The volcano displays the classic "overturned soup bowl" profile of Galápagos shield volcanoes. Its caldera is elongated in a NW-SE direction and formed during several episodes of collapse. Circumferential fissures surround the caldera and were instrumental in growth of the volcano. Reporting has been poor in this uninhabited western end of the archipelago, and even a 1981 eruption was not witnessed at the time. In 1968 the caldera floor dropped 350 m following a major explosive eruption. Subsequent eruptions, mostly from vents located on or near the caldera boundary faults, have produced lava flows inside the caldera as well as those in 1995 that reached the coast from a SW-flank vent. Collapse of a nearly 1 km3 section of the east caldera wall during an eruption in 1988 produced a debris-avalanche deposit that covered much of the caldera floor and absorbed the caldera lake.

Masaya

Nicaragua

11.985°N, 86.165°W; summit elev. 594 m

All times are local (unless otherwise noted)

Lava lake persists with lower temperatures during August 2019-January 2020

Masaya is a basaltic caldera located in Nicaragua and contains the Nindirí, San Pedro, San Juan, and Santiago craters. The currently active Santiago crater hosts a lava lake, which has remained active since December 2015 (BGVN 41:08). The primary source of information for this August 2019-January 2020 report comes from the Instituto Nicareguense de Estudios Territoriales (INETER) and satellite -based imagery and thermal data.

On 16 August, 13 September, and 11 November 2019, INETER took SO2 measurements by making a transect using a mobile DOAS spectrometer that sampled for gases downwind of the volcano. Average values during these months were 2,095 tons/day, 1,416 tons/day, and 1,037 tons/day, respectively. August had the highest SO2 measurements while those during September and November were more typical values.

Satellite imagery showed a constant thermal anomaly in the Santiago crater at the lava lake during August 2019 through January 2020 (figure 82). According to a news report, ash was expelled from Masaya on 15 October 2019, resulting in minor ashfall in Colonia 4 de Mayo (6 km NW). On 21 November thermal measurements were taken at the fumaroles and near the lava lake using a FLIR SC620 thermal camera (figure 83). The temperature measured 287°C, which was 53° cooler than the last time thermal temperatures were taken in May 2019.

Figure 83. Thermal measurements taken at Masaya on 21 November 2019 with a FLIR SC620 thermal camera that recorded a temperature of 287°C. Courtesy of INETER (Boletin Sismos y Volcanes de Nicaragua, Noviembre, 2019).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed intermittent low-power thermal anomalies compared to the higher-power ones before May 2019 (figure 84). The thermal anomalies were detected during August 2019 through January 2020 after a brief hiatus from early may to mid-June.

Figure 84. Thermal anomalies occurred intermittently at Masaya during 21 February 2019 through January 2020. Courtesy of MIROVA.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras caldera and is itself a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The Nindirí and Masaya cones, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6,500 years ago. Historical lava flows cover much of the caldera floor and there is a lake at the far eastern end. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals have caused health hazards and crop damage.

Reventador

Ecuador

0.077°S, 77.656°W; summit elev. 3562 m

All times are local (unless otherwise noted)

Reventador is an andesitic stratovolcano located in the Cordillera Real, Ecuador. Historical eruptions date back to the 16th century, consisting of lava flows and explosive events. The current eruptive activity has been ongoing since 2008 with previous activity including daily explosions with ash emissions, and incandescent block avalanches (BGVN 44:08). This report covers volcanism from August 2019 through January 2020 using information primarily from the Instituto Geofísico (IG-EPN), the Washington Volcano Ash Advisory Center (VAAC), and various infrared satellite data.

During August 2019 to January 2020, IG-EPN reported almost daily explosive eruptions and ash plumes. September had the highest average of explosive eruptions while January 2020 had the lowest (table 11). Ash plumes rose between a maximum of 1.2 to 2.5 km above the crater during this reporting period with the highest plume height recorded in December. The largest amount of SO2 gases produced was during the month of October with 502 tons/day. Frequently at night during this reporting period, crater incandescence was observed and was occasionally accompanied by incandescent block avalanches traveling as far as 900 m downslope from the summit of the volcano.

Table 11. Monthly summary of eruptive events recorded at Reventador from August 2019 through January 2020. Data courtesy of IG-EPN (August to January 2020 daily reports).

Month

Average Number of Explosions

Max plume height above the crater

Max SO2

Aug 2019

26

1.6 km

--

Sep 2019

32

1.7 km

428 tons/day

Oct 2019

29

1.3 km

502 tons/day

Nov 2019

25

1.2 km

432 tons/day

Dec 2019

25

2.5 km

331 tons/day

Jan 2020

12

1.7 km

--

During the month of August 2019, between 11 and 45 explosions were recorded every day, frequently accompanied by gas-and-steam and ash emissions (figure 119); plumes rose more than 1 km above the crater on nine days. On 20 August the ash plume rose to a maximum 1.6 km above the crater. Summit incandescence was seen at night beginning on 10 August, continuing frequently throughout the rest of the reporting period. Incandescent block avalanches were reported intermittently beginning that same night through 26 January 2020, ejecting material between 300 to 900 m below the summit and moving on all sides of the volcano.

Figure 119. An ash plume rising from the summit of Reventador on 1 August 2019. Courtesy of Radio La Voz del Santuario.

Throughout most of September 2019 gas-and-steam and ash emissions were observed almost daily, with plumes rising more than 1 km above the crater on 15 days, according to IG-EPN. On 30 September, the ash plume rose to a high of 1.7 km above the crater. Each day, between 18 and 72 explosions were reported, with the latter occurring on 19 September. At night, crater incandescence was commonly observed, sometimes accompanied by incandescent material rolling down every flank.

Elevated seismicity was reported during 8-15 October 2019 and almost daily gas-and-steam and ash emissions were present, ranging up to 1.3 km above the summit. Every day during this month, between 13 and 54 explosions were documented and crater incandescence was commonly observed at night. During November 2019, gas-and-steam and ash emissions rose greater than 1 km above the crater except for 10 days; no emissions were reported on 29 November. Daily explosions ranged up to 42, occasionally accompanied by crater incandescence and incandescent ejecta.

Washington VAAC notices were issued almost daily during December 2019, reporting ash plumes between 4.6 and 6 km altitude throughout the month and drifting in multiple directions. Each day produced 5-52 explosions, many of which were accompanied by incandescent blocks rolling down all sides of the volcano up to 900 m below the summit. IG-EPN reported on 11 December that a gas-and-steam and ash emission column rose to a maximum height of 2.5 km above the crater, drifting SW as was observed by satellite images and reported by the Washington VAAC.

Volcanism in January 2020 was relatively low compared to the other months of this reporting period. Explosions continued on a nearly daily basis early in the month, ranging from 20 to 51. During 5-7 January incandescent material ejected from the summit vent moved as block avalanches downslope and multiple gas-and-steam and ash plumes were produced (figures 120, 121, and 122). After 9 January the number of explosions decreased to 0-16 per day. Ash plumes rose between 4.6 and 5.8 km altitude, according to the Washington VAAC.

Figure 120. Night footage of activity on 5 (top) and 6 (bottom) January 2020 at the summit of Reventador, producing a dense, dark gray ash plume and ejecting incandescent material down multiple sides of the volcano. This activity is not uncommon during this reporting period. Courtesy of Martin Rietze, used with permission.

Figure 121. An explosion at Reventador on 7 January 2020, which produced a dense gray ash plume. Courtesy of Martin Rietze, used with permission.

Figure 122. Night footage of the evolution of an eruption on 7 January 2020 at the summit of Reventador, which produced an ash plume and ejected incandescent material down multiple sides of the volcano. Courtesy of Martin Rietze, used with permission.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed frequent and strong thermal anomalies within 5 km of the summit during 21 February 2019 through January 2020 (figure 123). In comparison, the MODVOLC algorithm reported 24 thermal alerts between August 2019 and January 2020 near the summit. Some thermal anomalies can be seen in Sentinel-2 thermal satellite imagery throughout this reporting period, even with the presence of meteorological clouds (figure 124). These thermal anomalies were accompanied by persistent gas-and-steam and ash plumes.

Figure 123. Thermal anomalies at Reventador persisted during 21 February 2019 through January 2020 as recorded by the MIROVA system (Log Radiative Power). Courtesy of MIROVA.

Figure 124. Sentinel-2 thermal satellite images of Reventador from August 2019 to January 2020 showing a thermal hotspot in the central summit crater summit. In the image on 7 January 2020, the thermal anomaly is accompanied by an ash plume. Courtesy of Sentinel Hub Playground.

Geologic Background. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic Volcán El Reventador stratovolcano rises to 3562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the east was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1300 m above the caldera floor to a height comparable to the caldera rim. It has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Pacaya

Guatemala

14.382°N, 90.601°W; summit elev. 2569 m

All times are local (unless otherwise noted)

Continuous explosions, small cone, and lava flows during August 2019-January 2020

Pacaya is a highly active basaltic volcano located in Guatemala with volcanism consisting of frequent lava flows and Strombolian explosions originating in the Mackenney crater. The previous report summarizes volcanism that included multiple lava flows, Strombolian activity, avalanches, and gas-and-steam emissions (BGVN 44:08), all of which continue through this reporting period of August 2019 to January 2020. The primary source of information comes from reports by the Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH) in Guatemala and various satellite data.

Strombolian explosions occurred consistently throughout this reporting period. During the month of August 2019, explosions ejected material up to 30 m above the Mackenney crater. These explosions deposited material that contributed to the formation of a small cone on the NW flank of the Mackenney crater. White and occasionally blue gas-and-steam plumes rose up to 600 m above the crater drifting S and W. Multiple incandescent lava flows were observed traveling down the N and NW flanks, measuring up to 400 m long. Small to moderate avalanches were generated at the front of the lava flows, including incandescent blocks that measured up to 1 m in diameter. Occasionally incandescence was observed at night from the Mackenney crater.

In September 2019 seismicity was elevated compared to the previous month, registering a maximum of 8,000 RSAM (Realtime Seismic Amplitude Measurement) units. White and occasionally blue gas-and-steam plumes that rose up to 1 km above the crater drifted generally S as far as 3 km from the crater. Strombolian explosions continued, ejecting material up to 100 m above the crater rim. At night and during the early morning, crater incandescence was observed. Incandescent lava flows traveled as much as 600 m down the N and NW flanks toward the Cerro Chino crater (figure 116). On 21 September two lava flows descended the SW flank. Constant avalanches with incandescent blocks measuring 1 m in diameter occurred from the front of many of these lava flows.

Figure 116. Webcam image of Pacaya on 25 September 2019 showing thermal signatures and the point of emission on the NNW flank at night using Landsat 8 (Nocturnal) imagery (left) and a daytime image showing the location of these lava effusions (right) along with gas-and-steam emissions from the active crater. Courtesy of INSIVUMEH.

Weak explosions continued through October 2019, ejecting material up to 75 m above the crater and building a small cone within the crater. White and occasionally blue gas-and-steam plumes rose 400-800 m above the crater, drifting W and NW and extending up to 4 km from the crater during the week of 26 October-1 November. Lava flows measuring up to 250 m long, originating from the Mackenney crater were descending the N and NW flanks (figure 117). Avalanches carrying large blocks 1 m in diameter commonly occurred at the front of these lava flows.

Figure 117. Photo of lava flows traveling down the flanks of Pacaya taken between 28 September 2019 and 4 October. Courtesy of INSIVUMEH (28 September 2019 to 4 October Weekly Report).

Continuing Strombolian explosions in November 2019 ejected material 15-75 m above the crater, which then contributed to the formation of the new cone. White and occasionally blue gas-and-steam plumes rose 100-600 m above the crater drifting in different directions and extending up to 2 km. Multiple lava flows from the Mackenney crater moving down all sides of the volcano continued, measuring 50-700 m long. Avalanches were generated at the front of the lava flows, often moving blocks as large as 1 m in diameter. The number of lava flows decreased during 2-8 November and the following week of 9-15 November no lava flows were observed, according to INSIVUMEH. During the week of 16-22 November, a small collapse occurred in the Mackenney crater and explosive activity increased during 16, 18, and 20 November, reaching RSAM units of 4,500. At night and early morning in late November crater incandescence was visible. On 24 November two lava flows descended the NW flank toward the Cerro Chino crater, measuring 100 m long.

During December 2019, much of the activity remained the same, with Strombolian explosions originating from two emission points in the Mackenney crater ejecting material 75-100 m above the crater; white and occasionally blue gas-and-steam plumes to 100-300 m above the crater drifted up to 1.5 km downwind to the S and SW. Lava flows descended the S and SW flanks reaching 250-600 m long (figure 118). On 29 December seismicity increased, reaching 5,000 RSAM units.

Figure 118. Lava flows moving to the S and SW at Pacaya on 31 December 2019. Courtesy of INSIVUMEH (28 December 2019 to 3 January 2020 Weekly Report).

Consistent Strombolian activity continued into January 2020 ejecting material 25-100 m above the crater. These explosions deposited material inside the Mackenney crater, contributing to the formation of a small cone. White and occasionally blue fumaroles consisting of mostly water vapor were observed drifting in different directions. At night, summit incandescence and lava flows were visible descending the N, NW, and S flanks with the flow on the NW flank traveling toward the Cerro Chino crater.

During August 2019 through January 2020, multiple lava flows and bright thermal anomalies (yellow-orange) within the crater were seen in Sentinel-2 thermal satellite imagery (figures 119 and 120). In addition, constant strong thermal anomalies were detected by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system during 21 February 2019 through January 2020 within 5 km of the summit (figure 121). A slight decrease in energy was seen from May to June and August to September. Energy increased again between November and December. According to the MODVOLC algorithm, 37 thermal alerts were recorded during August 2019 through January 2020.

Figure 121. The MIROVA thermal activity graph (log radiative power) at Pacaya during 21 February 2019 to January 2020 shows strong, frequent thermal anomalies through January with a slight decrease in energy between May 2019 to June 2019 and August 2019 to September 2019. Courtesy of MIROVA.

Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Alaid

Russia

50.861°N, 155.565°E; summit elev. 2285 m

All times are local (unless otherwise noted)

Volcanic tremor detected beginning on 31 October

On 4 November 2003 the Level of Concern Color Code was raised to Yellow due to volcanic tremor that began on 31 October. Weak seismicity continued through 7 November. Volcanic tremor during this time was 0.5-3.3 x 10-6 mps, and a large number of weak local events were registered. On satellite images the volcano was obscured by clouds all week.

The Kamchatkan Volcanic Eruption Response Team notes that Alaid is characterized by two types of eruptions: central crater eruptions and lateral eruptions. Central crater eruptions are stronger and more dangerous then the lateral ones. The strongest central crater eruptions of Alaid were in February 1793, June 1854, July 1860, 1894, and April 1981. The April 1981 eruption sent an ash plume to 8,000-9,000 m altitude that extended for more than 1,500 km (SEAN 06:04 and 06:05). Two eruptions in 1933-1934 and 1972 (CSLP Cards nos. 1405, 1406, 1410, and 1518) ejected ash columns 3 km high.

Geologic Background. The highest and northernmost volcano of the Kuril Islands, 2285-m-high Alaid is a symmetrical stratovolcano when viewed from the north, but has a 1.5-km-wide summit crater that is breached widely to the south. Alaid is the northernmost of a chain of volcanoes constructed west of the main Kuril archipelago. Numerous pyroclastic cones dot the lower flanks of this basaltic to basaltic-andesite volcano, particularly on the NW and SE sides, including an offshore cone formed during the 1933-34 eruption. Strong explosive eruptions have occurred from the summit crater beginning in the 18th century. Reports of eruptions in 1770, 1789, 1821, 1829, 1843, 1848, and 1858 were considered incorrect by Gorshkov (1970). Explosive eruptions in 1790 and 1981 were among the largest in the Kuril Islands during historical time.

Asosan

Japan

32.884°N, 131.104°E; summit elev. 1592 m

All times are local (unless otherwise noted)

Phreatic eruptions during 10-14 July cause ashfall 14 km away

Recent noteworthy activity at Aso consisted of elevated tremor in August 2002 and a phreatic eruption in July 2003. Seismicity recorded by the Japan Meteorological Agency (JMA) between January 2000 and April 2003 (table 8) was generally constant, with continuous volcanic tremor every month in addition to isolated tremor events. The number of tremor events was high through October 2000, during April 2002, and from August 2002 through March 2003. Also during this extended period, white plumes were observed approximately once a month, with two or more plumes occurring in July, October, and December 2002, and February and March 2003. These plumes were usually less than 500 m high.

Table 8. Seismicity at Aso between January 2000 and April 2003. The seismograph station is located ~13 km W of the summit. Courtesy of JMA.

Month

Number of volcanic earthquakes

Number of volcanic tremors

Jan 2000

19

1,466

Feb 2000

16

926

Mar 2000

73

1,232

Apr 2000

--

--

May 2000

39

537

Jun 2000

30

802

Jul 2000

29

1,234

Aug 2000

21

2,104

Sep 2000

36

1,445

Oct 2000

38

1,448

Nov 2000

43

202

Dec 2000

33

129

Jan 2001

51

60

Feb 2001

161

739

Mar 2001

76

537

Apr 2001

40

81

May 2001

40

85

Jun 2001

99

188

Jul 2001

84

282

Aug 2001

60

471

Sep 2001

40

86

Oct 2001

91

32

Nov 2001

52

17

Dec 2001

45

5

Jan 2002

38

5

Feb 2002

59

20

Mar 2002

20

20

Apr 2002

114

1,138

May 2002

91

14

Jun 2002

191

36

Jul 2002

238

37

Aug 2002

153

4,413

Sep 2002

144

1,438

Oct 2002

103

1,440

Nov 2002

652

3,391

Dec 2002

154

8,496

Jan 2003

122

6,981

Feb 2003

178

4,183

Mar 2003

92

1,965

Apr 2003

70

474

Activity during August 2002. For the first time since 1992, isolated volcanic tremor events occurred at a rate of more than 300 events/day in Naka-dake Crater 1. These events were recorded between 5 and 21 August and totalled nearly 4,000 (table 9), with the highest number, 340 events, on 15 August. During this period, the water temperature of the pool in the crater remained between 57 and 60°C. On 14 August, infrared cameras measured the maximum temperature of the southern crater wall at 307°C; this increased to 314°C the following week.

Activity during July 2003. JMA reported on 11 July 2003 that tephra had fallen at Aso that morning. According to the report, a tremor event with an intermediate amplitude was recorded at 1718 on 10 July. Staff from the Aso Weather Station confirmed that small amounts of tephra had been newly deposited at Hakoishi-Toge (Hakoishi Pass), ~ 6 km ENE of the Nakadake crater. Kazunori Watanabe (Kumamoto University) and other geologists surveyed the deposit on 11 July and estimated the total mass of ejected material at roughly 130 tons. Ash was deposited as far as 14 km from the crater. A small amount of fresh vesicular glass particles were noted in the ejecta under the microscope. According to Yasuaki Sudo (Aso Volcanological Laboratory, Kyoto University), who inspected the crater area, the event was a small phreatic eruption of mud. The deposit consisted of wet ash aggregates and was ~ 1 mm thick, even at the crater rim. A spray of mud was blown off the crater rim by strong winds to 10 km from the crater.

Seismic signals implied a series of small phreatic eruptions between 12 and 14 July. Then on 27 July continuous volcanic tremor started around 1400. Observations that day noted that the water in Crater 1 was gray and boiling in the center; the temperature of the water was 76°C.

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Bezymianny

Russia

55.972°N, 160.595°E; summit elev. 2882 m

All times are local (unless otherwise noted)

Rapid decrease in activity following the 26 July eruption

A large explosive eruption of Bezymianny on 26 July 2003 sent an ash plume 8-11 km high and 86 km long (BGVN 28:07). A later KVERT report noted that the active eruption phase lasted ~ 4 hours after beginning on 2057. Longer plumes on 27 July extended to 192 km, 217 km and ~ 250-300 km W of the vent. Probable pyroclastic deposits were identified on the SE flank.

No seismicity was registered during 27 July-3 August. The Color Code was lowered from Red to Orange on 28 July, and reduced to Yellow on 1 August. A 1-2-pixel thermal anomaly was detected on 1 August, and observers saw gas-and-steam plumes extending ~ 15 km NW on 2 August. On 8 August the hazard status was returned to Green. Clouds frequently obscured the volcano, but another gas-and-steam plume extended SE on 19 August when a 2-pixel thermal anomaly was also noted on satellite imagery. No further seismicity was recorded through 22 August, although large volcanic tremor at nearby Kliuchevskoi volcano would have masked smaller events.

Geologic Background. Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Cereme

Indonesia

6.895°S, 108.408°E; summit elev. 3039 m

All times are local (unless otherwise noted)

Volcanic seismicity that began in March increased in October

Data from the Volcanological Survey of Indonesia (VSI) indicated a tectonic and volcanic earthquake at Cereme on 25 March, followed by one more volcanic event on 28 March. Activity picked up on 2 April with three more volcanic events, with 17 events through 14 April. Daily highs of 8 and 11 events were recorded on 24 April and 3 May, respectively (2-4 May had 22). Seismicity remained generally low (0-3/day) until 29 events occurred on 7 October.

After a felt earthquake on 7 October, volcanic earthquakes increased. This increased seismicity was accompanied by elevated visually observed activity, resulting in the hazard status being upgraded to Alert Level 2 on 13 October. Seismic activity during 6-12 October consisted of 46 deep volcanic earthquakes and 15 shallow volcanic earthquakes; 36 deep volcanic events occurred the following week of 13-19 October. There was a felt earthquake on 19 October that lasted for 95.5 seconds (35 mm amplitude). Seismic activity declined during 20-26 October, when only seven deep volcanic earthquakes were recorded. The temperature measured at the Sangkan Hurip hotspring in late October was 48°C, unchanged from previous measurements.

Geologic Background. The symmetrical stratovolcano Cereme is located closer to the northern coast than other central Java volcanoes. A large crater elongated in an E-W direction, formed by multiple vents, caps the summit of Gunung Cereme, which was constructed on the northern rim of the 4.5 x 5 km Geger Halang caldera. A large landslide deposit to the north may be associated with the origin of the caldera, although collapse may rather be due to a voluminous explosive eruption (Newhall and Dzurisin, 1988). Eruptions have included explosive activity and lahars, primarily from the summit crater.

Fuego

Guatemala

14.473°N, 90.88°W; summit elev. 3763 m

All times are local (unless otherwise noted)

Explosive eruptions and lava flows through October

Explosive and effusive activity, last reported through January 2003 (BGVN 28:01) has continued through October 2003. Plumes identified on satellite imagery between April and September 2003 were described in aviation advisories issued by the Washington Volcanic Ash Advisory Center (VAAC). Regular reports of daily activity provided by the Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH) on their website have been summarized for many days in the second half of October.

Activity during April-September 2003. The Washington VAAC reported that on 28 April 2003 Fuego generated intermittent ash eruptions. One cloud was observed at ~ 7 km altitude moving SW at 19-29 km/hour. On 2 May the VAAC reported possible ash around the summit, but as of 1515, none was visible. INSIVUMEH indicated that although Fuego was active with explosions, most ash was confined to near the summit.

On 29 June INSIVUMEH reported a moderate eruption during 1745-2200 that consisted mainly of lava effusion. Lava flows were observed on the E flank, in the Lajas, Jute, and Barranca Honda ravines. Avalanches generated sounds similar to a locomotive, with strong rumblings and acoustic waves. Fuego's Observatory 2, on the SW flank, reported 2 cm of ashfall. Ashfall also occurred in San Pedro Yepocapa, Patulul Suchitepequez, Cocales, and villages W and SW of the volcano. At about 2335 there was a reduction in seismic activity at the Fuego 3 station.

INSIVUMEH reported on 1 July that explosive activity continued with weak to sometimes strong explosions ejecting grayish ash up to 900 m above the crater, with occasional degassing sounds and rumblings. Pyroclastic-flow material moved into the W-flank Seca and Santa Teresa valleys, 1.5 km from the village of Sangre de Cristo. A pyroclastic flow was reported by the Washington VAAC at 1130 on 9 July. INSIVUMEH reported strong explosions with ash to 2 km above the summit, a plume extending 5-7 km W, and ashfall to the W and SW. GOES-12 imagery showed a 3.7-km-wide plume extending ~ 11 km W.

The Washington VAAC reported on 7 August that a brief puff of ash was ejected at about 1600; the small plume moved to the NW and dissipated by 1745. On 28 September the Washington VAAC, based on visible and multi-spectral IR techniques, reported an ash eruption at about 1100. This plume, which was ~ 5 x 5 km, moved S toward the coast and was no longer discernable on imagery by 1400. A second ash emission between 1415 and 1432, with an approximate altitude of 6 km, was partially obscured by clouds.

Activity during 15-30 October 2003. On 15 October INSIVUMEH reported the continuation of eruptive activity, with degassing and small rumbling sounds. Incandescence was seen above the crater at night. The ejected ash was dispersed around the volcanic edifice. A small eruption that began at 0007 on 17 October ended at 0040 after five moderate explosive pulses, each 2-3 minutes in duration, generated thick columns of grayish ash ~ 1,500 m high. Before and after this eruptive event moderate and strong explosions caused rumbling and shock waves felt at the OVFGO and FG2 observatories. Small incandescent avalanches moved towards the Santa Teresa valley.

Harmonic tremor was registered at the FG3 station at 1630 on 20 October. On 21 October, INSIVUMEH reported explosions after 0350. The majority were strong, expelling abundant incandescent material. Ash columns caused small and moderate avalanches, mainly in the Santa Teresa and Trinidad valleys, and occasionally in the Taniluyá. Shock waves were felt by communities around the volcano. Slight ashfall occurred in the Morelia and Santa Lucia villages located 7 and 10 km, respectively, SSW of the active crater.

On 23 October, INSIVUMEH reported moderate, weak and occasionally strong explosions producing grayish and blackish plumes up to one km high. Moderate and strong explosions generated rumbling and lava flows that traveled toward the Santa Teresa and Trinidad valleys. Ashfall occurred in the upper portion of the Fuego-Acatenango complex. At 0945 a strong explosion, lasting 1.5 minutes, produced a thick ash cloud that reached a height of ~ 1 km and dispersed to the SW. Two short pulses lasting 45-60 minutes between 1200-1300 and 1800-1900 on 23 October generated a series of 7-9 moderate explosions that produced a grayish column to ~ 1 km over the central crater.

A strong explosion at 0910 on 27 October was preceded by five moderate explosions at intervals of 3-7 minutes that produced gas clouds and ash 700 m high. The first event produced a heavy ash column of a height of ~ 1 km which dispersed to the SW. An explosion at 0625 caused a pyroclastic flow toward the Trinidad and Santa Teresa valleys, and produced light ashfall in the village of Sangre de Cristo. On 29 October INSIVUMEH reported predominantly weak and moderate explosions 1-3.5 minutes long with gas-and-ash columns up to 1 km high. The last of these produced ashfall, shock waves felt at OVFGO, and avalanches of incandescent material toward the Santa Teresa and Trinidad valleys.

On 30 October an effusive eruption during 2300-0600 produced incandescent lava fountains 75-100 m high with pulses of 5-6 minutes, changing to fountains ~ 50 m high and 15-20 minutes long. A short lava flow descended SW from the crater rim, reaching ~ 250 m in length and splitting into three short branches. Short avalanches and pyroclastic flows descended to the top of the Santa Teresa valley. The eruption produced moderate to weak sounds lasting ~ 2 minutes. At dawn, a thick fumarolic plume was observed blowing NW. There was no ash emission during this activity, but at 0625 hours a small explosion sent a column of gas and ash ~ 400 m high. The seismic station at FG3 registered harmonic tremor (2-4 mm amplitude).

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is also one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between Fuego and Acatenango to the north. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at the mostly andesitic Acatenango. Eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Gamalama

Indonesia

0.8°N, 127.33°E; summit elev. 1715 m

All times are local (unless otherwise noted)

Small ash explosions August to early October; seismicity normal by mid-October

A series of explosive eruptions on 31 July 2003 produced ashfall and pyroclastic flows (BGVN 28:07). Several small ash explosions occurred throughout August and September (BGVN 28:09). Activity was similar during 29 September-5 October 2003, with white gas emissions rising 25-100 m and some small ash explosions. Volcanic seismicity consisted of one deep earthquake, two shallow earthquakes, and 24 emission events. Activity remained low the following week, 6-12 October, with gas emissions rising 25-50 m. The number of daily seismic events this week had returned to normal levels, so the hazard status was downgraded to Alert Level 1 (on a scale of 1-4) on 13 October.

Geologic Background. Gamalama is a near-conical stratovolcano that comprises the entire island of Ternate off the western coast of Halmahera, and is one of Indonesia's most active volcanoes. The island was a major regional center in the Portuguese and Dutch spice trade for several centuries, which contributed to the thorough documentation of Gamalama's historical activity. Three cones, progressively younger to the north, form the summit. Several maars and vents define a rift zone, parallel to the Halmahera island arc, that cuts the volcano. Eruptions, recorded frequently since the 16th century, typically originated from the summit craters, although flank eruptions have occurred in 1763, 1770, 1775, and 1962-63.

Ijen

Indonesia

8.058°S, 114.242°E; summit elev. 2769 m

All times are local (unless otherwise noted)

Shallow volcanic earthquakes and continuous tremor recorded in October

The hazard status of Ijen was upgraded to Alert Level 2 (on a scale of 1-4) on 8 October. Seismicity the week of 6-12 October comprised four deep volcanic earthquakes, 21 shallow volcanic earthquakes, one emission event, and continuous tremor (0.5-2 mm amplitude). Only 16 shallow volcanic earthquakes were recorded the following week, along with continuous tremor (0.5-2 mm amplitude). Continuous tremor (0.5-4 mm amplitude) was recorded during 20-26 October, a week when the number of shallow volcanic events increased to 30. Gas plumes emitted from the crater rose up to 150 m high during October.

Geologic Background. The Ijen volcano complex at the eastern end of Java consists of a group of small stratovolcanoes constructed within the large 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the caldera rim is buried by post-caldera volcanoes, including Gunung Merapi, which forms the high point of the complex. Immediately west of the Gunung Merapi stratovolcano is the historically active Kawah Ijen crater, which contains a nearly 1-km-wide, turquoise-colored, acid lake. Picturesque Kawah Ijen is the world's largest highly acidic lake and is the site of a labor-intensive sulfur mining operation in which sulfur-laden baskets are hand-carried from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of cones forms an E-W zone across the southern side of the caldera. Coffee plantations cover much of the caldera floor, and tourists are drawn to its waterfalls, hot springs, and volcanic scenery.

Karangetang

Indonesia

2.781°N, 125.407°E; summit elev. 1797 m

All times are local (unless otherwise noted)

White gas emissions and glow during October, but decreased seismicity

Explosive activity has been common at Karangetang in recent years, producing ashfall and lava avalanches as recently as May and June 2003 (BGVN 28:05 and 28:07). However, Karangetang was not included in reports by the Volcanological Survey of Indonesia (VSI) between 16 June and 28 September 2003. A report for the week of 29 September-5 October indicated that there had been a decrease in multiphase and emissions earthquakes compared to the previous week (table 9). At that time white gas emissions were observed rising 400 m above the S crater and 50 m above the N crater. Red glow was seen at night over the S crater that week. No lava avalanches occurred. Similar observations were reported through 19 October. Although surface observations of activity were consistent, seismic data showed that shallow volcanic earthquakes increased and emission events decreased during 6-19 October. The hazard status remained at Alert Level 2 (on a scale of 1-4) through at least 19 October.

Table 9. Seismicity at Karangetang during 2 June-19 October 2003. No data was available between 16 June and 28 September. Courtesy of VSI.

Date

Deep volcanic (A-type)

Shallow volcanic (B-type)

Multiphase

Emission

Tectonic

02 Jun-08 Jun 2003

11

348

233

46

26

09 Jun-15 Jun 2003

32

438

228

21

20

29 Sep-05 Oct 2003

15

84

50

121

38

06 Oct-12 Oct 2003

19

103

33

74

32

13 Oct-19 Oct 2003

18

135

54

72

33

Geologic Background. Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi island. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented in the historical record (Catalog of Active Volcanoes of the World: Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

Krakatau

Indonesia

6.102°S, 105.423°E; summit elev. 155 m

All times are local (unless otherwise noted)

Increased volcanic seismicity in August

A report of activity at Krakatau for the period 18-24 August was provided by the Volcanological Survey of Indonesia. There was increase in volcanic earthquakes during this time, while tectonic earthquakes decreased. No visual observations were made due to foggy weather. Seismicity consisted of 12 deep volcanic earthquakes, 56 shallow volcanic earthquakes, and three tectonic events. The hazard status was at Alert Level 2 (on a scale of 1-4).

Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Lewotobi

Indonesia

8.542°S, 122.775°E; summit elev. 1703 m

All times are local (unless otherwise noted)

Explosions and ashfall during June-July; seismicity stops in early September

Explosive ash eruptions from the summit crater of Lewotobi sent dark gray plumes 300-350 m high between 2 June and 13 July. Detonation sounds accompanied explosions on 3, 5, and 6 June. Ash fell in the villages of Bawalatang, Duang, and Boru in early June, and was reported at the volcano observatory post in early July. Ash explosions continued during 14-20 July with plumes rising 150 m above the summit. Poor weather conditions prevented observations in late July, although seismic records indicated continued activity; no reports were available for August. In early September an ash plume was reported to rise 25 m above the crater.

Seismicity during June and July was dominated by emissions events, but included tremor, explosion, and shallow volcanic earthquakes (table 2). Early September seismicity consisted of a high number of shallow volcanic events and some deep volcanic earthquakes, but all seismicity ceased after 3 September. Only four tectonic earthquakes were detected after this date, during 6-19 October. The 29 September-5 October report noted an ash plume rising to 25 m above the crater, but over the next two weeks the 25-m-high plume was described as gas emissions. The hazard status was downgraded to Alert Level 1 (on a scale of 1-4) the week of 13-19 October.

Table 2. Seismicity at Lewotobi, 2 June-19 October 2003. Note that no seismicity was recorded after 3 September 2003. Courtesy of VSI.

Date

Deep Volcanic

Shallow Volcanic

Explosion

Emission

Tremor

Tectonic

02 Jun-08 Jun 2003

0

13

7

29

20

12

09 Jun-15 Jun 2003

0

24

--

40

33

9

30 Jun-06 Jul 2003

0

8

14

26

11

3

07 Jul-13 Jul 2003

0

16

10

52

4

1

14 Jul-20 Jul 2003

4

17

19

24

10

4

21 Jul-27 Jul 2003

1

10

5

25

5

4

28 Jul-03 Aug 2003

0

9

8

20

6

3

01 Sep-03 Sep 2003*

27

257

0

0

0

5

Geologic Background. The Lewotobi "husband and wife" twin volcano (also known as Lewetobi) in eastern Flores Island is composed of the Lewotobi Lakilaki and Lewotobi Perempuan stratovolcanoes. Their summits are less than 2 km apart along a NW-SE line. The conical Lakilaki has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has erupted only twice in historical time. Small lava domes have grown during the 20th century in both of the crescentic summit craters, which are open to the north. A prominent flank cone, Iliwokar, occurs on the E flank of Perampuan.

Lokon-Empung

Indonesia

1.358°N, 124.792°E; summit elev. 1580 m

All times are local (unless otherwise noted)

Small gas plume; high but variable shallow volcanic seismicity

The hazard status at Lokon-Empung throughout the report period of 2 June-19 October was at Alert Level 2 (on a scale of 1-4). Between 2 June and 5 October a white gas plume consistently rose 25-50 m above Tompaluan crater. The gas plume rose slightly higher, to 75 m, during the following two weeks. Seismicity remained above normal background levels during this time, with some variation (table 7). Shallow volcanic earthquakes increased in late July, but by September the weekly count was lower than in early July, eventually reaching a low the week of 15-21 September when no such events were detected. Seismicity quickly returned to high values of 138-209 shallow events per week in October.

Table 7. Seismicity at Lokon-Empung, 2 June-19 October 2003. Data was not available for 16-29 June and 04-31 August. Courtesy of VSI.

Date

Deep volcanic (A-type)

Shallow volcanic (B-type)

Tectonic

02 Jun-08 Jun 2003

13

45

20

09 Jun-15 Jun 2003

25

88

27

30 Jun-06 Jul 2003

18

81

19

07 Jul-13 Jul 2003

17

48

15

14 Jul-20 Jul 2003

9

91

19

21 Jul-27 Jul 2003

25

232

21

28 Jul-03 Aug 2003

16

157

10

01 Sep-07 Sep 2003

11

44

11

08 Sep-14 Sep 2003

7

36

20

15 Sep-21 Sep 2003

12

0

22

22 Sep-28 Sep 2003

34

22

20

29 Sep-05 Oct 2003

33

209

24

06 Oct-12 Oct 2003

5

159

14

13 Oct-19 Oct 2003

24

138

14

Geologic Background. The twin volcanoes Lokon and Empung, rising about 800 m above the plain of Tondano, are among the most active volcanoes of Sulawesi. Lokon, the higher of the two peaks (whose summits are only 2 km apart), has a flat, craterless top. The morphologically younger Empung volcano to the NE has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century, but all subsequent eruptions have originated from Tompaluan, a 150 x 250 m wide double crater situated in the saddle between the two peaks. Historical eruptions have primarily produced small-to-moderate ash plumes that have occasionally damaged croplands and houses, but lava-dome growth and pyroclastic flows have also occurred. A ridge extending WNW from Lokon includes Tatawiran and Tetempangan peak, 3 km away.

Masaya

Nicaragua

11.985°N, 86.165°W; summit elev. 594 m

All times are local (unless otherwise noted)

This report summarizes the activity at Masaya during June-September 2003. Activity was generally constant, with fumarole temperature measurements similar to those from previous months (BGVN 28:08). In June, July, and August, during visits made every two weeks, Jaime Cárdenas of Masaya Volcano National Park measured the fumarole temperatures at the Comalito and San Fernando craters (table 4). No changes were observed from previous months. During these months, seismic tremor remained constant with 20 units RSAM. No earthquakes were registered, but on both 21 June and 21 July landslides were reported in the Santiago crater. In September, temperatures obtained from the Santiago crater with a Pyrometer were 187°C and 123°C. It was noted during this visit that the lava sounded like ocean waves, and incandescence was observed at night. Temperatures at El Comalito remained moderate.

Table 4. Temperatures recorded at the El Comalito (EC) and San Fernando (SF) fumaroles of Masaya, 10 June-22 September 2003. All temperatures are in degrees Celsius. Courtesy INETER.

Date

EC 1

EC 2

EC 3

EC 4

EC 5

EC 6

SF 1

SF 2

SF 3

SF 4

10 Jun 2003

65.4

74.5

76.8

72.5

73.4

60.2

59.2

54.8

57.2

55.8

28 Jun 2003

66.4

75.4

78.4

73.6

73.8

60.4

60.2

55.6

58.8

56.7

12 Jul 2003

55

76

78.2

74

73.6

60

60

60.2

59.5

57

26 Jul 2003

66.8

78.4

79.4

75.6

74.2

61

61.2

61.4

60.2

58.2

15 Aug 2003

66.6

78.2

79.5

76

74.5

61.5

59.7

59.7

57.2

56.2

29 Aug 2003

67.8

75.6

76.6

74.8

76.4

64.2

59.3

57.4

56.9

57

22 Sep 2003

68.6

72.3

68.3

65.2

--

--

--

--

--

--

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras caldera and is itself a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The Nindirí and Masaya cones, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6,500 years ago. Historical lava flows cover much of the caldera floor and there is a lake at the far eastern end. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals have caused health hazards and crop damage.

Miyakejima

Japan

34.094°N, 139.526°E; summit elev. 775 m

All times are local (unless otherwise noted)

Continued seismicity and regular gas-and-steam plumes

Volcanic activity at Miyake-jima since the eruption during the summer of 2000 (BGVN 25:07) has continued at lower levels through August 2003. The flux of SO2 gas remained high (~ 4, 000-9, 000 tons/day), and has been nearly constant since October 2002 (figure 20). A compilation of seismic data and plume observations through April 2003 (table 3) documents this continuing activity. Plume heights following the June-September 2000 activity have not been greater than 2.2 km above the summit (table 3), and their color has been described as white or grayish white.

Figure 20. SO2 flux at Miyake-jima during August 2000-August 2003. Triangles along the timeline indicate explosions. Courtesy of the Geological Survey of Japan and the Japan Meteorological Agency.

Table 3. Summary of seismicity and plume observations at Miyake-jima, January 2000-April 2003. All reported plumes originated from the summit crater, and were described as either white (W), light white (LW), grayish white (GW), or gray (G). No months during this time had more than six plumes observed on any single day. Data courtesy of JMA.

Month

Volcanic earthquakes

Max. Plume Height (km) (date)

Plume Color (date)

Jan 2000

2

--

--

Feb 2000

4

--

--

Mar 2000

1

--

--

Apr 2000

No JMA report received this month

May 2000

3

--

--

Jun 2000

> 13,840

--

--

Jul 2000

> 24,494

1.5 (8, 14)

W (8) colored (14, 15)

Aug 2000

> 10,175

14 (18)

Mix of white and colored almost daily all after 10th

Sep 2000

146

3.5 (26) frequently above 1

W (almost daily), C (3, 24, 27)

Oct 2000

16

2.7 (10)

W

Nov 2000

5

2.5 (26)

W

Dec 2000

6

2.0 (22, 27)

W

Jan 2001

214

1.8 (22, 31)

W, GW (11)

Feb 2001

260

2.0 (17)

W

Mar 2001

299

2.0 (2, 16, 24)

W, GW (19)

Apr 2001

191

2.0 (4)

W

May 2001

707

2.2 (6)

W, G (27)

Jun 2001

192

2.2 (10)

W, G (3, 10)

Jul 2001

249

1.6 (16, 21)

W, G (10)

Aug 2001

306

2.0 (24, 25, 27, 28)

W

Sep 2001

234

3.0 (16)

W

Oct 2001

116

1.5 (16, 21, 22, 24, 29, 31)

W, GW

Nov 2001

124

2.0 (20)

W, GW (1)

Dec 2001

123

1.7 (29)

W

Jan 2002

41

2.0 (6)

W, GW

Feb 2002

88

1.7 (14)

W, GW

Mar 2002

71

1.2 (16, 28)

W, GW (31)

Apr 2002

104

1.0 (10)

W, GW (2, 3)

May 2002

265

1.5 (29)

W

Jun 2002

176

0.8 (9)

W, GW (15)

Jul 2002

78

0.8 (27)

W

Aug 2002

45

1.0 (3)

W

Sep 2002

57

1.5 (4)

W

Oct 2002

47

1.0 (6, 30)

W, GW (8)

Nov 2002

55

1.0 (6, 29)

W

Dec 2002

66

0.8 (28)

W

Jan 2003

202

1.0 (25)

W

Feb 2003

313

0.8 (13)

W

Mar 2003

212

1.2 (28)

W

Apr 2003

450

1.0 (28)

W

The number of monthly earthquakes was very low (1-4/month) until late June through early September 2000. Except for 5 May 2001 when 447 volcanic earthquakes occurred, daily totals have been less than 50. Monthly earthquake totals since August 2000 have been less than 300, except for May 2001 (707) and April 2003 (450). Volcanic tremor also began in July 2000 and became continuous in September 2000. Tremor through April 2003 totaled less than 500 events per month, except for May 2001, when 1, 362 events were recorded (444 on the 22nd). The unusually high seismicity noted in May 2001 corresponded to a period of continuous steam plumes with abundant SO2 content (BGVN 27:03), after which SO2 flux declined (figure 2).

Seismicity at Miyake-jima is recorded by three seismographs maintained by the Japan Meterological Agency (JMA): station "A" is ~ 1.9 km NNE of the summit at 530 m elevation, station "AKOC" is ~ 4.6 km W at 42 m elevation, and station "RST" is ~ 1.9 km SSE at 463 m elevation.

Geologic Background. The circular, 8-km-wide island of Miyakejima forms a low-angle stratovolcano that rises about 1100 m from the sea floor in the northern Izu Islands about 200 km SSW of Tokyo. The basaltic volcano is truncated by small summit calderas, one of which, 3.5 km wide, was formed during a major eruption about 2500 years ago. Parasitic craters and vents, including maars near the coast and radially oriented fissure vents, dot the flanks of the volcano. Frequent historical eruptions have occurred since 1085 CE at vents ranging from the summit to below sea level, causing much damage on this small populated island. After a three-century-long hiatus ending in 1469, activity has been dominated by flank fissure eruptions sometimes accompanied by minor summit eruptions. A 1.6-km-wide summit caldera was slowly formed by subsidence during an eruption in 2000; by October of that year the crater floor had dropped to only 230 m above sea level.

Nyamuragira

DR Congo

1.408°S, 29.2°E; summit elev. 3058 m

All times are local (unless otherwise noted)

Long-period earthquake swarms

During the 3-month period from 2 August to 8 November 2003, seismicity in the Nyamuragira area was dominated by long-period (LP) events localized along a main NNE-SSW fracture between Nyamuragira and Nyiragongo volcanoes. Intermittent swarms of LP events (60-80 events each time) occurred on Nyamuragira two to three times per week. A larger swarm was observed on 23 July (100 LP events). This activity remained fairly stable for the whole period. Earthquakes related to fracturing continued, mainly S of Nyiragongo (N of Lake Kivu ) and NE of Nyamuragira. No noticeable deformation change has been recorded along the fracture system.

Geologic Background. Africa's most active volcano, Nyamuragira, is a massive high-potassium basaltic shield about 25 km N of Lake Kivu. Also known as Nyamulagira, it has generated extensive lava flows that cover 1500 km2 of the western branch of the East African Rift. The broad low-angle shield volcano contrasts dramatically with the adjacent steep-sided Nyiragongo to the SW. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Historical eruptions have occurred within the summit caldera, as well as from the numerous fissures and cinder cones on the flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Historical lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.

Nyiragongo

DR Congo

1.52°S, 29.25°E; summit elev. 3470 m

All times are local (unless otherwise noted)

Lava lake growing through pit-wall collapses; environmental damage

During the 3-month period from 2 August to 8 November 2003, volcanic activity was concentrated inside the Nyiragongo crater. An almost permanently boiling lava lake occupies the crater at the depth of 700 m. Although the level of the lake inside the crater seems to remain constant, its size is slowly growing due to collapses of the pit walls. Degassing has been significant, marked by a large gas plume above the crater which is generally blown W by the prevailing winds and extends several tens of kilometers. The impact of this activity on the environment is growing; inside the National Park, a 50 km2 area of forest was totally destroyed by volcanic gases and acid rains, and a zone with 50% destruction covers more than 700 km2, affecting crops such as potatoes, corn, beans, and bananas. In the same areas significant fluoride pollution has been detected, and tanks collecting rain water are showing fluoride concentrations up to 23 mg/l (WHO tolerance = 1.5 mg/l).

In the Nyiragongo area, long-period events are commonly detected but at reduced number and are mainly located NW and SW of the volcano. Seismicity is largely dominated by permanent tremor generated by the activity of the lava lake. Earthquakes related to fracturing continue, mainly S of Nyiragongo and NE of Nyamuragira (~ 15 km NW of Nyiragongo). No noticeable deformation change has been recorded along the fracture system between the two volcanoes.

Geologic Background. One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Pacaya

Guatemala

14.382°N, 90.601°W; summit elev. 2569 m

All times are local (unless otherwise noted)

Frequent steam plumes

Although incandescence from the long-term lava lake ended after June 2001, SO2 emission rates remained high when measured in January 2002 (BGVN 27:07). On 30 May 2002, the Washington Volcanic Ash Advisory Center (VAAC) received a report from Guatemala City indicating that Pacaya was active. Satellite imagery showed possible low-level ash near the summit. A very thin SW-drifting plume was again visible in satellite imagery on 17 June 2002, but the composition of the plume was unknown. A faint hotspot at the summit was also visible on infrared imagery. Visual observation on the afternoon 24 August 2002 from the SW showed copious white steam emissions from the summit crater (figure 34).

The Washington VAAC reported that on 5 July 2003 at 0715, a very thin ash and/or gas plume was visible on satellite imagery at an altitude of ~ 3 km extending ~ 7.5 km SW. By 1430 the plume was no longer visible, possibly obscured by thunderstorm clouds in the area. INSIVUMEH reported that only steam was emitted. Visible imagery on 9 August 2003 showed a narrow plume below 3 km altitude extending SW from the volcano, but its composition was unknown.

Reports provided by INSIVUMEH during the latter half of October 2003 indicated that during 15-21 October constant steam and abundant emissions of water and gas were being blown to the NNW and W of the volcano. These emissions continued through the end of the month. On 23 October, during periods of visibility, observers saw a line of off-white smoke across the S flank, which was dispersed in the area of the lava field near the Chupadero and the Caracol rivers. The next day observers saw a heavy column of off-white smoke rising ~ 600 m over the MacKenney crater. The plume continued through 27 October, but only to a height of ~ 400 m. The heavy gaseous cloud continued at the same height through 30 October.

Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

San Cristobal

Nicaragua

12.702°N, 87.004°W; summit elev. 1745 m

All times are local (unless otherwise noted)

Intermittent ash emissions between August 2002 and September 2003

This report summarizes the recorded activity at San Cristóbal during August 2002-September 2003. Reports from Instituto Nicaragüense de Estudios Territoriales (INETER) include observations from frequent visits to the volcano.

August-December 2002. During August-December 2002, abundant gas emanations were accompanied by small gas explosions. Incandescence was frequently observed. Seismicity was relatively high, but fluctuated from month to month (table 2). On 12 August, ash emissions with columns up to 800 m high were observed. More ash explosions were reported on 17 and 21 August. Gas emissions and small ash explosions continued in September, and incandescence was observed during 1-7 September. A strong explosion was reported on 6 October, and a dark gas column was observed. Throughout the month gas emissions were abundant, occasionally with columns to 600 m high. Temperatures at the South Point and El Zopilote fumaroles increased in October from the previous month. Gas emissions and ash explosions continued in November and December, with increased activity on 22 November and 16 December. Trees and fruit plants were affected by the gases in the community of Las Banderas. At the end of December, a volcano observer discovered that the path to the volcano was blocked by a deposit of sand-sized material.

Table 2. Number of earthquakes at San Cristóbal between August 2002 and June 2003. No data was available during November 2002 due to technical problems. Courtesy of INETER.

Month

Number of earthquakes

Aug 2002

2,183

Sep 2002

2,792

Oct 2002

1,017

Nov 2002

--

Dec 2002

200-250 / day

Jan 2003

5,671

Feb 2003

2,595

Mar 2003

5,329

Apr 2003

1,713

May 2003

5,491

Jun 2003

4,855

January-March 2003. Activity decreased in the first few months of 2003. No changes were observed in the crater in January, and temperatures increased only at two fumaroles; those temperatures were low again in February. On 19 February the observer heard loud sustained noises and noted that the crater walls were colored green and yellow, indicating the presence of sulfur.

April-September 2003. Between April and September, fumarole temperatures were measured on each of the monthly visits to San Cristóbal, and showed very little change. The highest temperatures were generally found at South Point and were between 91 and 95°C. At El Munecho temperatures varied between 81 and 91°C, and at El Conejo between 77 and 86°C. Temperatures remained moderate at the other fumaroles.

Gas emissions were noted in particular between 20 and 23 April, days on which there were small increases in tremor; on 10 May gas emissions were strong enough to impede a visit. Activity increased in June, with abundant ash and gas emissions noted on 17 and 21 June. On 21 June incandescence was noted, and strong rumbling was heard in the evening. On 13 July gas emissions were dense, followed during 14-23 July by a dark column. Seismicity dropped from more than 350 events per day to 69 events on 3 July. By 9 July, only eight events per day were recorded; tremor remained constant at 35 RSAM units.

Gas emissions remained constant through August and September, with reports of gas explosions during a visit on 10 August and abundant gases during the 17 September visit. The strong noises and sounds of gas pressure being released decreased over these months, and no noise was noted on the September visit. Seismicity was very low in August and September, with no earthquakes and very low tremors in August, and only six earthquakes in September.

Geologic Background. The San Cristóbal volcanic complex, consisting of five principal volcanic edifices, forms the NW end of the Marrabios Range. The symmetrical 1745-m-high youngest cone, named San Cristóbal (also known as El Viejo), is Nicaragua's highest volcano and is capped by a 500 x 600 m wide crater. El Chonco, with several flank lava domes, is located 4 km W of San Cristóbal; it and the eroded Moyotepe volcano, 4 km NE of San Cristóbal, are of Pleistocene age. Volcán Casita, containing an elongated summit crater, lies immediately east of San Cristóbal and was the site of a catastrophic landslide and lahar in 1998. The Plio-Pleistocene La Pelona caldera is located at the eastern end of the complex. Historical eruptions from San Cristóbal, consisting of small-to-moderate explosive activity, have been reported since the 16th century. Some other 16th-century eruptions attributed to Casita volcano are uncertain and may pertain to other Marrabios Range volcanoes.

Santa Maria

Guatemala

14.757°N, 91.552°W; summit elev. 3745 m

All times are local (unless otherwise noted)

Explosions, pyroclastic flows, and night glow in October

Long term eruptive activity at the Santiaguito lava-dome complex of Santa María has continued during 2003 following lahars, explosions, and pyroclastic flows reported during much of 2002 (BGVN 28:05). Plumes identified on satellite imagery between February and September 2003 were described in aviation advisories issued by the Washington Volcanic Ash Advisory Center (VAAC). Regular reports of daily activity provided by the Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH) on their website have been summarized for many days in the second half of October.

Satellite observations, February-September 2003. Based on GOES-8 imagery the Washington VAAC reported that explosions occurred during the evening of 16 February 2003 and the following morning. Plumes rose to 600 m above the summit, forming an ash plume that was visible on satellite imagery. Imagery from GOES-12 indicated an eruption at about 1330 on 23 July. The plume moved W and had largely dissipated by 1615 after extending ~ 80 km. Washington VAAC reported that the volcano had been active in recent days and that INSIVUMEH had reported an ash column rising to ~ 4.6 km altitude, causing ashfall on farms W of the summit.

The Washington VAAC identified another ash cloud in GOES-12 imagery on 14 August from 0715 through 0745 that was ~ 25 km long and 5 km wide. On 28 September the Washington VAAC reported an ash emission, again based on GOES-12 imagery, that reached an estimated 4.3 km altitude. By 1532 the plume appeared to have detached from the summit and begun to slowly dissipate.

Activity observed during October 2003. Weak and moderate explosions on 15 October continued to expel gray ash to heights of 300-600 m, dispersing to the W and SW. At night blocks of incandescent lava were seen down to the base of the Caliente dome. On 17 October, as during 16 October, most of the nearly 50 explosions were considered moderate, generating avalanches of block lava and ash on the SSW flanks and NE of the Caliente cone. However, at 1745 on 16 October, a strong explosion caused the collapse of a sector of the SW flank of the crater, forming a pyroclastic flow that lasted more than 3 minutes and stopped as it neared the front of the active lava flow ~ 4 km S of Santiaguito.

On 21 October, explosions sent gas-and-ash columns 200-700 m high, which were dispersed by winds to the W, causing slight ashfall of very fine particles to fall in the dome complex. During the night of 22-23 October incandescence on the edge of the crater rim of Caliente cone was observed. Avalanches lasting 3-4 minutes continued with abundant block lava and ash descending primarily down the SSW flank with a minor component to the NE. The ash columns tended to be carried W, causing fine ashfall in sparsely populated mountainous areas. On 24 October there were 26 moderate explosions, 41 weak ones, and about 20 avalanches of lava blocks and ash originating from the S edge of the lava dome in the Caliente cone crater and from the edge of the active lava flow.

During the night of 27 October incandescence along the edge of the lava dome was observed, and weak white fumarolic emissions reached ~ 200 m above the crater in the morning; explosions and avalanches persisted. On 29 October, predominantly moderate and weak explosions produced columns 200-700 m high, and very fine ash fell in nearby mountainous areas. Many of the moderate explosions produced avalanches of block lava and ash to the NE and SW. On 30 October, three small collapses of large blocks occurred from the crater rim, and more than a dozen avalanches, each preceded by explosions and lasting 2-3 minutes, produced abundant fine ash that partially covered the S flank.

Geologic Background. Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing W towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Semeru

Indonesia

8.108°S, 112.922°E; summit elev. 3657 m

All times are local (unless otherwise noted)

Frequent ash explosions continue through October

Frequent ash explosions at Semeru during 29 September-26 October 2003 produced white-gray ash plumes 400-500 m over the summit. The hazard status remained at Alert Level 2 (on a scale of 1-4) during this time. Although tectonic earthquakes, tremor events, shallow volcanic earthquakes, and avalanches were all detected seismically, the record was dominated by explosions (table 14). Explosions over this 4-week period averaged 95 per day, or one every 15 minutes.

Table 14. Seismicity at Semeru, 29 September-26 October 2003. Four shallow volcanic earthquakes were also detected during 6-12 October. Courtesy of VSI.

Date

Explosion

Avalanche

Tremor

Tectonic

29 Sep-05 Oct 2003

636

20

9

4

06 Oct-12 Oct 2003

567

10

--

7

13 Oct-19 Oct 2003

687

19

22

4

20 Oct-26 Oct 2003

768

16

3

11

Geologic Background. Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

Sheveluch

Russia

56.653°N, 161.36°E; summit elev. 3283 m

All times are local (unless otherwise noted)

Ash eruptions, lava dome growth, steam plumes, and thermal anomalies

Eruptive activity continued during August-October 2003, including growth of a lava dome in the active crater. Seismicity remained above background levels, and weak, shallow earthquakes were recorded throughout the period. Slightly higher seismic activity was recorded on 30 October with magnitudes in the range of 2.0-2.4. Short-lived eruptions each week sent ash-and-gas plumes to heights of 100-1,500 m above the dome. Thermal anomalies were often recorded by US and Russian satellites.

Weak volcanic tremor was detected during 22-31 August. Tremor was accompanied by gas-and-steam plumes as high as 800 m during 26-27 August, and 2-4-pixel thermal anomalies on 26-30 August. Small thermal anomalies (1-4 pixels) and 500-800-m-high steam plumes were common through 19 September, with an 11-pixel anomaly on the 18th. Similar small thermal anomalies and plumes appeared again during 25-30 September. Thermal anomalies continued to be detected during 1-4, 7-8, 10-12, 16-20, 26, and 29-30 October. Steam plumes were also common, with varying heights of 100-800 m. Small steam plumes and a 1-pixel anomaly occurred 2-3 November.

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Soputan

Indonesia

1.112°N, 124.737°E; summit elev. 1785 m

All times are local (unless otherwise noted)

Ash explosion and lava flows on 31 August

Increased activity during 18-22 July 2003 at Soputan consisted of frequent ash explosions and large glowing lava avalanches (BGVN 28:08). Seismicity from August through mid-October was dominated by avalanche events, with a few tectonic earthquakes (table 4). White gas emissions in this period were commonly seen rising 25-50 m above the crater, but were also reported as high as 1,000 m in late August and September. On 31 August there was ash explosion accompanied by ejection of incandescent material. The ash column reached 1,000 m above the summit. Lava flowed 750 m down the SW slope, and some descended to the N. Volcanic tremor that week (18-31 August) had an amplitude of 10-38 mm. The hazard status remained at Alert Level 2 (on a scale of 1-4) through 19 October.

Geologic Background. The Soputan stratovolcano on the southern rim of the Quaternary Tondano caldera on the northern arm of Sulawesi Island is one of Sulawesi's most active volcanoes. The youthful, largely unvegetated volcano is located SW of Riendengan-Sempu, which some workers have included with Soputan and Manimporok (3.5 km ESE) as a volcanic complex. It was constructed at the southern end of a SSW-NNE trending line of vents. During historical time the locus of eruptions has included both the summit crater and Aeseput, a prominent NE-flank vent that formed in 1906 and was the source of intermittent major lava flows until 1924.

Soufriere Hills

United Kingdom

16.72°N, 62.18°W; summit elev. 915 m

All times are local (unless otherwise noted)

Low-level seismicity; ash venting 30 September-1 October

Activity at Soufriére Hills remained at a relatively low level from mid-September into early November 2003. Seismicity consisted mostly of hybrid earthquakes and rockfall signals (table 49). Access continues to be prohibited to some areas after the major dome collapse and explosive activity of 12-13 July 2003 (BGVN 28:08), and there is a maritime exclusion zone around the S part of the island extending 3.7 km beyond the coastline from Trant's Bay in the E to Isles Bay on the W coast.

Table 49. Summary of seismic activity at Soufriére Hills, 5 September-7 November 2003. No volcano-tectonic earthquakes were recorded during this period, but one long-period rockfall event occurred 23-31 October. Courtesy of the Montserrat Volcano Observatory.

Date

Rockfall

Long-period

Hybrid

05 Sep-12 Sep 2003

2

3

27

12 Sep-19 Sep 2003

9

4

20

19 Sep-26 Sep 2003

13

1

20

26 Sep-03 Oct 2003

4

--

241

03 Oct-10 Oct 2003

1

--

15

10 Oct-17 Oct 2003

12

--

9

17 Oct-24 Oct 2003

8

2

12

24 Oct-31 Oct 2003

11

2

19

31 Oct-07 Nov 2003

8

--

16

During the week of 12-19 September, no growth of the new lava dome was observed. Activity was at a slightly higher level during the week of 26 September-3 October, especially hybrid earthquakes, most of which occurred in a swarm between 1100 and 2100 on 27 September. Some of the hybrids could be located at 2-4 km depth. A period of low-amplitude tremor was also recorded between 0800 on 30 September and 0400 on 1 October coincident with vigorous ash venting, which resulted in ash clouds reaching 2,000-2,500 m altitude and drifting W over Plymouth. Observations on 30 September and 3 October suggested that no new dome growth had occurred.

From 3 October to 7 November, activity returned to a low level. A period of low-amplitude tremor was recorded between 3 and 8 October, and some mudflow signals were also recorded during periods of heavy rain. The tremor coincided with light ash venting. Visibility was poor during this period, so no direct observations of the summit area were possible. The dome was observed clearly on 23 October and a volume survey was carried out from Galways and Perches Mountains. The small dome that extruded in July 2003 had not grown further and appeared to be stagnant, with alteration and degradation occurring such that it appears to be breaking up. The pit crater associated with the explosions of July 2003 had widened slightly, although this was thought to be due to passive slumping of material. Sulfur dioxide and hydrogen chloride emission rates were high during several days around 13-15 October and on 22 October (table 50). An observation flight on 28 October yielded clear views of the scar area and the W scar wall. No changes were observed in the morphology of the scar and no new lava was observed in the vent area.

According to the Washington VAAC, on 1 November resuspended ash was seen in satellite imagery. The ash was moving N to NNW at ~10 km/hour from Montserrat between Nevis and Antigua, and the resuspended ash was concentrated in a narrow plume.

Geologic Background. The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. The volcano is flanked by Pleistocene complexes to the north and south. English's Crater, a 1-km-wide crater breached widely to the east by edifice collapse, was formed about 2000 years ago as a result of the youngest of several collapse events producing submarine debris-avalanche deposits. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits, including those from an eruption that likely preceded the 1632 CE settlement of the island, allowing cultivation on recently devegetated land to near the summit. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but no historical eruptions were recorded until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.

Unnamed

Tonga

18.325°S, 174.365°W; summit elev. -40 m

All times are local (unless otherwise noted)

A felsic shallow marine explosive eruption from a previously unknown volcano along the Tofua volcanic arc (Tonga) in September-October 2001 (BGVN 26:11 and 27:01) produced floating pumice rafts in Fiji in November 2001, approximately one month after it occurred. These sea-rafted pumice are the only recorded output of this subaqueous eruption at a remote location where direct observations are limited.

A new influx of sea-rafted pumice reached the eastern coast of Australia in October 2002 (figure 4), approximately one year after the eruption was first indicated by seismic activity and pumice stranding in Fiji. Pumice was stranded along at least two-thirds (>2,000 km) of the coastline of eastern Australia, extending from N of Townsville to Sydney. Typical amounts of pumice initially stranded on beaches were 500-4,000 individual clasts per m2; a minimum volume estimate of pumice deposited along the eastern Australian coastline is 1.25 x 105 m3. Most stranded pumice clasts are 1-5 cm diameter, although some outsized clasts are up to 10 cm. Many clasts were fouled by a variety of organisms, and dark algal coverings were common to all clasts that concealed the primary character of the pumice (figure 5). This is in contrast to pumice stranded on beaches in Fiji ~ 1 month after the eruption, which were clean of fouling organisms. Fouling organisms include algae, Bryozoa, serpulid worms, corals and, oysters with goose barnacles particularly abundant.

Figure 4. Map of the southwest Pacific Ocean showing the location of the unnamed volcano in the Tofua volcanic arc that erupted in September-October 2001 producing the pumice rafts. The general dispersal trajectory of the sea-rafted pumice is shown by the dashed line, and the pumice reached the eastern Australian coastline ~ 1 year after the eruption. Courtesy of Scott Bryan.

The pumice have a low phenocryst content (< 5% modal) with the phenocryst assemblage consisting of calcic plagioclase (An88-74), pigeonite (En45 Fs46 Wo9), augite (En35 Fs29 Wo36), and titanomagnetite. Preliminary petrographic observations in dicate that the pumice is compositionally homogenous, although there is considerable variation in vesicularity within and between clasts. Tubed pumice is a minor but distinctive clast type. The pumice, like previously stranded pumice on the Great Barrier Reef (Bryan, 1968, 1971), is low-K dacite in composition (table 2), characterized by low alkalis and high iron and silica. This composition is similar to other pumice-forming eruptions from the Tonga region (Bryan, 1968).

Table 2. Major element data on sea-rafted pumice clasts from eastern Australia, 2002. Samples HI1 and GC1: major element data for whole pumice clasts determined by the atomic absorption method of silicate rock analysis using Inductively-Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) at the University of Queensland. Samples P1 and P2 (n=3 for both): averaged pumice glass compositions analysed at the Centre for Microscopy & Microanalysis, University of Queensland, using a JEOL 8800-L (wavelength dispersive) electron microprobe. Analyses were performed with an accelerating voltage of 15 kV and with a probe current of 15 nA and a probe diameter of 10 microns to avoid volatilisation of alkali elements. Courtesy of Scott Bryan and Alex Cook.

Geologic Background. A submarine volcano along the Tofua volcanic arc was first observed in September 2001. The newly discovered volcano lies NW of the island of Vava'u about 35 km S of Fonualei and 60 km NE of Late volcano. The site of the eruption is along a NNE-SSW-trending submarine plateau with an approximate bathymetric depth of 300 m. T-phase waves were recorded on 27-28 September 2001, and on the 27th local fishermen observed an ash-rich eruption column that rose above the sea surface. No eruptive activity was reported after the 28th, but water discoloration was documented during the following month. In early November rafts and strandings of dacitic pumice were reported along the coast of Kadavu and Viti Levu in the Fiji Islands. The depth of the summit of the submarine cone following the eruption determined to be 40 m during a 2007 survey; the crater of the 2001 eruption was breached to the E.

Atmospheric Effects

The enormous aerosol cloud from the March-April 1982 eruption of Mexico's El Chichón persisted for years in the stratosphere, and led to the Atmospheric Effects section becoming a regular feature of the Bulletin. Descriptions of the initial dispersal of major eruption clouds remain with the individual eruption reports, but observations of long-term stratospheric aerosol loading will be found in this section.

Special Announcements

Additional Reports

Reports are sometimes published that are not related to a Holocene volcano. These might include observations of a Pleistocene volcano, earthquake swarms, or floating pumice. Reports are also sometimes published in which the source of the activity is unknown or the report is determined to be false. All of these types of additional reports are listed below by subregion and subject.

Additional Reports (database)

Press reports of Somalia's first historical eruption were likely in error

11/1999 (BGVN 24:11) False Report of Sea of Marmara Eruption

UFO adherent claims new volcano in Sea of Marmara

05/2003 (BGVN 28:05) Har-Togoo

Fumaroles and minor seismicity since October 2002

12/2005 (BGVN 30:12) Elgon

False report of activity; confusion caused by burning dung in a lava tube

False Report of Mount Pinokis Eruption (Philippines) — August 1997

False Report of Mount Pinokis Eruption

Philippines

7.975°N, 123.23°E; summit elev. 1510 m

All times are local (unless otherwise noted)

False report of volcanism intended to exclude would-be gold miners

In discussing the week ending on 12 September, "Earthweek" (Newman, 1997) incorrectly claimed that a volcano named "Mount Pinukis" had erupted. Widely read in the US, the dramatic Earthweek report described terrified farmers and a black mushroom cloud that resembled a nuclear explosion. The mountain's location was given as "200 km E of Zamboanga City," a spot well into the sea. The purported eruption had received mention in a Manila Bulletin newspaper report nine days earlier, on 4 September. Their comparatively understated report said that a local police director had disclosed that residents had seen a dormant volcano showing signs of activity.

In response to these news reports Emmanuel Ramos of the Philippine Institute of Volcanology and Seismology (PHIVOLCS) sent a reply on 17 September. PHIVOLCS staff had initially heard that there were some 12 alleged families who fled the mountain and sought shelter in the lowlands. A PHIVOLCS investigation team later found that the reported "families" were actually individuals seeking respite from some politically motivated harassment. The story seems to have stemmed from a local gold rush and an influential politician who wanted to use volcanism as a ploy to exclude residents. PHIVOLCS concluded that no volcanic activity had occurred. They also added that this finding disappointed local politicians but was much welcomed by the residents.

PHIVOLCS spelled the mountain's name as "Pinokis" and from their report it seems that it might be an inactive volcano. There is no known Holocene volcano with a similar name (Simkin and Siebert, 1994). No similar names (Pinokis, Pinukis, Pinakis, etc.) were found listed in the National Imagery and Mapping Agency GEOnet Names Server (http://geonames.nga.mil/gns/html/index.html), a searchable database of 3.3 million non-US geographic-feature names.

The Manila Bulletin report suggested that Pinokis resides on the Zamboanga Peninsula. The Peninsula lies on Mindanao Island's extreme W side where it bounds the Moro Gulf, an arm of the Celebes Sea. The mountainous Peninsula trends NNE-SSW and contains peaks with summit elevations near 1,300 m. Zamboanga City sits at the extreme end of the Peninsula and operates both a major seaport and an international airport.

[Later investigation found that Mt. Pinokis is located in the Lison Valley on the Zamboanga Peninsula, about 170 km NE of Zamboanga City and 30 km NW of Pagadian City. It is adjacent to the two peaks of the Susong Dalaga (Maiden's Breast) and near Mt. Sugarloaf.]

False Report of Somalia Eruption (Somalia) — December 1997

False Report of Somalia Eruption

Somalia

3.25°N, 41.667°E; summit elev. 500 m

All times are local (unless otherwise noted)

Press reports of Somalia's first historical eruption were likely in error

Xinhua News Agency filed a news report on 27 February under the headline "Volcano erupts in Somalia" but the veracity of the story now appears doubtful. The report disclosed the volcano's location as on the W side of the Gedo region, an area along the Ethiopian border just NE of Kenya. The report had relied on the commissioner of the town of Bohol Garas (a settlement described as 40 km NE of the main Al-Itihad headquarters of Luq town) and some or all of the information was relayed by journalists through VHF radio. The report claimed the disaster "wounded six herdsmen" and "claimed the lives of 290 goats grazing near the mountain when the incident took place." Further descriptions included such statements as "the volcano which erupted two days ago [25 February] has melted down the rocks and sand and spread . . . ."

Giday WoldeGabriel returned from three weeks of geological fieldwork in SW Ethiopia, near the Kenyan border, on 25 August. During his time there he inquired of many people, including geologists, if they had heard of a Somalian eruption in the Gedo area; no one had heard of the event. WoldeGabriel stated that he felt the news report could have described an old mine or bomb exploding. Heavy fighting took place in the Gedo region during the Ethio-Somalian war of 1977. Somalia lacks an embassy in Washington DC; when asked during late August, Ayalaw Yiman, an Ethiopian embassy staff member in Washington DC also lacked any knowledge of a Somalian eruption.

A Somalian eruption would be significant since the closest known Holocene volcanoes occur in the central Ethiopian segment of the East African rift system S of Addis Ababa, ~500 km NW of the Gedo area. These Ethiopian rift volcanoes include volcanic fields, shield volcanoes, cinder cones, and stratovolcanoes.

False Report of Sea of Marmara Eruption (Turkey) — November 1999

False Report of Sea of Marmara Eruption

Turkey

40.683°N, 29.1°E; summit elev. 0 m

All times are local (unless otherwise noted)

UFO adherent claims new volcano in Sea of Marmara

Following the Ms 7.8 earthquake in Turkey on 17 August (BGVN 24:08) an Email message originating in Turkey was circulated, claiming that volcanic activity was observed coincident with the earthquake and suggesting a new (magmatic) volcano in the Sea of Marmara. For reasons outlined below, and in the absence of further evidence, editors of the Bulletin consider this a false report.

The report stated that fishermen near the village of Cinarcik, at the E end of the Sea of Marmara "saw the sea turned red with fireballs" shortly after the onset of the earthquake. They later found dead fish that appeared "fried." Their nets were "burned" while under water and contained samples of rocks alleged to look "magmatic."

No samples of the fish were preserved. A tectonic scientist in Istanbul speculated that hot water released by the earthquake from the many hot springs along the coast in that area may have killed some fish (although they would be boiled rather than fried).

The phenomenon called earthquake lights could explain the "fireballs" reportedly seen by the fishermen. Such effects have been reasonably established associated with large earthquakes, although their origin remains poorly understood. In addition to deformation-triggered piezoelectric effects, earthquake lights have sometimes been explained as due to the release of methane gas in areas of mass wasting (even under water). Omlin and others (1999), for example, found gas hydrate and methane releases associated with mud volcanoes in coastal submarine environments.

The astronomer and author Thomas Gold (Gold, 1998) has a website (Gold, 2000) where he presents a series of alleged quotes from witnesses of earthquakes. We include three such quotes here (along with Gold's dates, attributions, and other comments):

(A) Lima, 30 March 1828. "Water in the bay 'hissed as if hot iron was immersed in it,' bubbles and dead fish rose to the surface, and the anchor chain of HMS Volage was partially fused while lying in the mud on the bottom." (Attributed to Bagnold, 1829; the anchor chain is reported to be on display in the London Navy Museum.)

(B) Romania, 10 November 1940. ". . . a thick layer like a translucid gas above the surface of the soil . . . irregular gas fires . . . flames in rhythm with the movements of the soil . . . flashes like lightning from the floor to the summit of Mt Tampa . . . flames issuing from rocks, which crumbled, with flashes also issuing from non-wooded mountainsides." (Phrases used in eyewitness accounts collected by Demetrescu and Petrescu, 1941).

(C) Sungpan-Pingwu (China), 16, 22, and 23 August 1976. "From March of 1976, various large anomalies were observed over a broad region. . . . At the Wanchia commune of Chungching County, outbursts of natural gas from rock fissures ignited and were difficult to extinguish even by dumping dirt over the fissures. . . . Chu Chieh Cho, of the Provincial Seismological Bureau, related personally seeing a fireball 75 km from the epicenter on the night of 21 July while in the company of three professional seismologists."

Yalciner and others (1999) made a study of coastal areas along the Sea of Marmara after the Izmet earthquake. They found evidence for one or more tsunamis with maximum runups of 2.0-2.5 m. Preliminary modeling of the earthquake's response failed to reproduce the observed runups; the areas of maximum runup instead appeared to correspond most closely with several local mass-failure events. This observation together with the magnitude of the earthquake, and bottom soundings from marine geophysical teams, suggested mass wasting may have been fairly common on the floor of the Sea of Marmara.

Despite a wide range of poorly understood, dramatic processes associated with earthquakes (Izmet 1999 apparently included), there remains little evidence for volcanism around the time of the earthquake. The nearest Holocene volcano lies ~200 km SW of the report location. Neither Turkish geologists nor scientists from other countries in Turkey to study the 17 August earthquake reported any volcanism. The report said the fisherman found "magmatic" rocks; it is unlikely they would be familiar with this term.

The motivation and credibility of the report's originator, Erol Erkmen, are unknown. Certainly, the difficulty in translating from Turkish to English may have caused some problems in understanding. Erkmen is associated with a website devoted to reporting UFO activity in Turkey. Photographs of a "magmatic rock" sample were sent to the Bulletin, but they only showed dark rocks photographed devoid of a scale on a featureless background. The rocks shown did not appear to be vesicular or glassy. What was most significant to Bulletin editors was the report author's progressive reluctance to provide samples or encourage follow-up investigation with local scientists. Without the collaboration of trained scientists on the scene this report cannot be validated.

Har-Togoo (Mongolia) — May 2003

Har-Togoo

Mongolia

48.831°N, 101.626°E; summit elev. 1675 m

All times are local (unless otherwise noted)

Fumaroles and minor seismicity since October 2002

In December 2002 information appeared in Mongolian and Russian newspapers and on national TV that a volcano in Central Mongolia, the Har-Togoo volcano, was producing white vapors and constant acoustic noise. Because of the potential hazard posed to two nearby settlements, mainly with regard to potential blocking of rivers, the Director of the Research Center of Astronomy and Geophysics of the Mongolian Academy of Sciences, Dr. Bekhtur, organized a scientific expedition to the volcano on 19-20 March 2003. The scientific team also included M. Ulziibat, seismologist from the same Research Center, M. Ganzorig, the Director of the Institute of Informatics, and A. Ivanov from the Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences.

Geological setting. The Miocene Har-Togoo shield volcano is situated on top of a vast volcanic plateau (figure 1). The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Pliocene and Quaternary volcanic rocks are also abundant in the vicinity of the Holocene volcanoes (Devyatkin and Smelov, 1979; Logatchev and others, 1982). Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Figure 1. Photograph of the Har-Togoo volcano viewed from west, March 2003. Courtesy of Alexei Ivanov.

Observations during March 2003. The name of the volcano in the Mongolian language means "black-pot" and through questioning of the local inhabitants, it was learned that there is a local myth that a dragon lived in the volcano. The local inhabitants also mentioned that marmots, previously abundant in the area, began to migrate westwards five years ago; they are now practically absent from the area.

Acoustic noise and venting of colorless warm gas from a small hole near the summit were noticed in October 2002 by local residents. In December 2002, while snow lay on the ground, the hole was clearly visible to local visitors, and a second hole could be seen a few meters away; it is unclear whether or not white vapors were noticed on this occasion. During the inspection in March 2003 a third hole was seen. The second hole is located within a 3 x 3 m outcrop of cinder and pumice (figure 2) whereas the first and the third holes are located within massive basalts. When close to the holes, constant noise resembled a rapid river heard from afar. The second hole was covered with plastic sheeting fixed at the margins, but the plastic was blown off within 2-3 seconds. Gas from the second hole was sampled in a mechanically pumped glass sampler. Analysis by gas chromatography, performed a week later at the Institute of the Earth's Crust, showed that nitrogen and atmospheric air were the major constituents.

Figure 2. Photograph of the second hole sampled at Har-Togoo, with hammer for scale, March 2003. Courtesy of Alexei Ivanov.

The temperature of the gas at the first, second, and third holes was +1.1, +1.4, and +2.7°C, respectively, while air temperature was -4.6 to -4.7°C (measured on 19 March 2003). Repeated measurements of the temperatures on the next day gave values of +1.1, +0.8, and -6.0°C at the first, second, and third holes, respectively. Air temperature was -9.4°C. To avoid bias due to direct heating from sunlight the measurements were performed under shadow. All measurements were done with Chechtemp2 digital thermometer with precision of ± 0.1°C and accuracy ± 0.3°C.

Inside the mouth of the first hole was 4-10-cm-thick ice with suspended gas bubbles (figure 5). The ice and snow were sampled in plastic bottles, melted, and tested for pH and Eh with digital meters. The pH-meter was calibrated by Horiba Ltd (Kyoto, Japan) standard solutions 4 and 7. Water from melted ice appeared to be slightly acidic (pH 6.52) in comparison to water of melted snow (pH 7.04). Both pH values were within neutral solution values. No prominent difference in Eh (108 and 117 for ice and snow, respectively) was revealed.

Two digital short-period three-component stations were installed on top of Har-Togoo, one 50 m from the degassing holes and one in a remote area on basement rocks, for monitoring during 19-20 March 2003. Every hour 1-3 microseismic events with magnitude <2 were recorded. All seismic events were virtually identical and resembled A-type volcano-tectonic earthquakes (figure 6). Arrival difference between S and P waves were around 0.06-0.3 seconds for the Har-Togoo station and 0.1-1.5 seconds for the remote station. Assuming that the Har-Togoo station was located in the epicentral zone, the events were located at ~1-3 km depth. Seismic episodes similar to volcanic tremors were also recorded (figure 3).

Figure 3. Examples of an A-type volcano-tectonic earthquake and volcanic tremor episodes recorded at the Har-Togoo station on 19 March 2003. Courtesy of Alexei Ivanov.

Conclusions. The abnormal thermal and seismic activities could be the result of either hydrothermal or volcanic processes. This activity could have started in the fall of 2002 when they were directly observed for the first time, or possibly up to five years earlier when marmots started migrating from the area. Further studies are planned to investigate the cause of the fumarolic and seismic activities.

At the end of a second visit in early July, gas venting had stopped, but seismicity was continuing. In August there will be a workshop on Russian-Mongolian cooperation between Institutions of the Russian and Mongolian Academies of Sciences (held in Ulan-Bator, Mongolia), where the work being done on this volcano will be presented.

Geologic Background. The Miocene Har-Togoo shield volcano, also known as Togoo Tologoy, is situated on top of a vast volcanic plateau. The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Elgon (Uganda) — December 2005

Elgon

Uganda

1.136°N, 34.559°E; summit elev. 3885 m

All times are local (unless otherwise noted)

False report of activity; confusion caused by burning dung in a lava tube

An eruption at Mount Elgon was mistakenly inferred when fumes escaped from this otherwise quiet volcano. The fumes were eventually traced to dung burning in a lava-tube cave. The cave is home to, or visited by, wildlife ranging from bats to elephants. Mt. Elgon (Ol Doinyo Ilgoon) is a stratovolcano on the SW margin of a 13 x 16 km caldera that straddles the Uganda-Kenya border 140 km NE of the N shore of Lake Victoria. No eruptions are known in the historical record or in the Holocene.

On 7 September 2004 the web site of the Kenyan newspaper The Daily Nation reported that villagers sighted and smelled noxious fumes from a cave on the flank of Mt. Elgon during August 2005. The villagers' concerns were taken quite seriously by both nations, to the extent that evacuation of nearby villages was considered.

The Daily Nation article added that shortly after the villagers' reports, Moses Masibo, Kenya's Western Province geology officer visited the cave, confirmed the villagers observations, and added that the temperature in the cave was 170°C. He recommended that nearby villagers move to safer locations. Masibo and Silas Simiyu of KenGens geothermal department collected ashes from the cave for testing.

Gerald Ernst reported on 19 September 2004 that he spoke with two local geologists involved with the Elgon crisis from the Geology Department of the University of Nairobi (Jiromo campus): Professor Nyambok and Zacharia Kuria (the former is a senior scientist who was unable to go in the field; the latter is a junior scientist who visited the site). According to Ernst their interpretation is that somebody set fire to bat guano in one of the caves. The fire was intense and probably explains the vigorous fuming, high temperatures, and suffocated animals. The event was also accompanied by emissions of gases with an ammonia odor. Ernst noted that this was not surprising considering the high nitrogen content of guano—ammonia is highly toxic and can also explain the animal deaths. The intense fumes initially caused substantial panic in the area.

It was Ernst's understanding that the authorities ordered evacuations while awaiting a report from local scientists, but that people returned before the report reached the authorities. The fire presumably prompted the response of local authorities who then urged the University geologists to analyze the situation. By the time geologists arrived, the fuming had ceased, or nearly so. The residue left by the fire and other observations led them to conclude that nothing remotely related to a volcanic eruption had occurred.

However, the incident emphasized the problem due to lack of a seismic station to monitor tectonic activity related to a local triple junction associated with the rift valley or volcanic seismicity. In response, one seismic station was moved from S Kenya to the area of Mt. Elgon so that local seismicity can be monitored in the future.